Documentation: Census 2010
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Publisher: U.S. Census Bureau
Survey: Census 2010
Document: Summary File 1 Technical Documentation
citation:
Social Explorer, U.S. Census Bureau; 2010 Census of Population and Housing, Summary File 1: Technical Documentation, Issued June 2011.
Summary File 1 Technical Documentation
Appendix A. Geographic Terms and Concepts
Introduction
This document provides definitions of geographic terms and concepts as well as a description of the different methods used to present information for geographic entities in U.S. Census Bureau data products. This document contains definitions for all geographic area terms and concepts recognized by the Census Bureau and that may appear in any Census Bureau product presenting demographic and housing data (geographic terms and concepts unique to the economic census and other specialized surveys and censuses are not included in this document).

The inclusion of a particular term or concept in this document does not imply that data for that geographic entity or attribute appear in each data product. For instance, data for tribal census tracts and tribal block groups will appear only in products providing data according to the American Indian Nation-based geographic hierarchy (see Figure A-2). As another example, because urban areas are defined on the basis of decennial census population counts, data for urban areas do not appear in initial decennial census data products. In addition, the description of both the hierarchical and inventory approaches to presenting data for geographic entities does not imply that both formats are used in each data product.

Geographic Presentation of Data
In Census Bureau data products, geographic entities usually are presented in a hierarchical arrangement or as an inventory listing.

Hierarchical Presentation
A hierarchical geographic presentation shows the geographic entities in a superior/subordinate structure. This structure is derived from the legal, administrative, or areal relationships of the entities. The hierarchical structure is depicted in report tables by means of indentation. For computer-readable media, the hierarchy is shown in the descriptive name applied to a summary level, with the hierarchy in order separated by hyphens. An example of hierarchical presentation is the census geographic hierarchy consisting of census block, within block group, within census tract, within place, within county subdivision, within county, within state. Graphically, this is shown as:

State
 County
  County subdivision
   Place (or part)
    Census tract (or part)
     Block group (or part)
      Block

Figure A-1, which is a diagram of the geographic hierarchy, presents this information as a series of nesting relationships. For example, a line joining the lower-level entity place and the higher-level entity state means that a place cannot cross a state boundary; a line linking census tract and county means that a census tract cannot cross a county line; and so forth. There is no implied hierarchy between different line tracks; for example, census tract nests within county, but it may cross a county subdivision boundary even though county subdivision also nests within county.

Inventory Presentation
An inventory presentation of geographic entities is one in which all entities of the same type are shown in alphabetical, code, or geographic sequence, without reference to their hierarchical relationships. Generally, an inventory presentation shows totals for entities that may be split in a hierarchical presentation, such as place, census tract, or block group. An example of a series of inventory presentations is state, followed by all the counties in that state, followed by all the places in that state. Graphically, this is shown as:

State

County A
County B
County C

Place X
Place Y
Place Z

Nation-Based Hierarchies
Exceptions to the standard hierarchical presentation occur for entities that do not necessarily nest within states, most notably American Indian, Alaska Native, and Native Hawaiian areas and core based statistical areas.

American Indian, Alaska Native, and Native Hawaiian Area (AIANNHA) Hierarchy
Because federally recognized American Indian areas can cross state lines, a separate American Indian, Alaska Native, and Native Hawaiian area (AIANNHA) hierarchy exists for these areas. For instance, the following American Indian entities can cross state lines: federally recognized American Indian reservations and/or off-reservation trust lands, tribal subdivisions, tribal designated statistical areas, tribal census tracts, and tribal block groups. National summary data for American Indian reservations or statistical areas may be presented as an alphabetical listing of names followed by the state portions of each area. Also, a tribal census tract or tribal block group may be located in more than one state or county. Data for tribal census tracts and tribal block groups are presented only in Census Bureau products utilizing the AIANNHA hierarchy and are not present in products utilizing the standard census geographic hierarchy.

The diagram in Figure A-2 shows geographic relationships among geographic entities in the AIANNHA hierarchy. It does not show the geographic levels county, county subdivision, and place, among others, because AIANNHAs do not necessarily nest within them.

Definitions of Geographic Entities, Terms, and Concepts
The definitions below are for geographic entities and concepts that the Census Bureau includes in its standard data products. Not all entities, terms, and concepts are shown in any one data product.
American Indian, Alaska Native, and Native Hawaiian Area
There are both legal and statistical American Indian, Alaska Native, and Native Hawaiian areas (AIANNHAs) for which the Census Bureau provides data. The legal entities consist of federally recognized American Indian reservations and off-reservation trust land areas, the tribal subdivisions that can divide these entities, state-recognized American Indian reservations, Alaska Native regional corporations, and Hawaiian home lands. The statistical entities are Alaska Native village statistical areas, Oklahoma tribal statistical areas, tribal designated statistical areas, and state designated tribal statistical areas. Statistical tribal subdivisions can exist within Oklahoma tribal statistical areas. In all cases, these areas are mutually exclusive in that no AIANNHA can overlap another tribal entity, except for tribal subdivisions, which by definition subdivide some American Indian entities, and Alaska Native village statistical areas, which exist within Alaska Native regional corporations. In cases where more than one tribe claims jurisdiction over an area, the Census Bureau creates a joint-use area as a separate entity to define this area of dual claims. The following provides more detail about each of the various AIANNHAs.

Legal Entities
Alaska Native regional corporations (ANRCs) were created pursuant to the Alaska Native Claims Settlement Act (ANCSA) (Pub. L. 92-203, 85 Stat. 688 [1971]; 43 U.S.C. 1602 et seq. [2000]), enacted in 1971 as a " Regional Corporation" and organized under the laws of the state of Alaska to conduct both the for-profit and non-profit affairs of Alaska Natives within a defined region of Alaska. For the Census Bureau, ANRCs are considered legal geographic entities. Twelve ANRCs cover the entire state of Alaska except for the area within the Annette Island Reserve (a federally recognized American Indian reservation under the governmental authority of the Metlakatla Indian Community). A thirteenth ANRC represents Alaska Natives who do not live in Alaska and do not identify with any of the twelve corporations. The Census Bureau does not provide data for this thirteenth ANRC because it has no defined geographic extent and thus, it does not appear in the TIGER/Line® shapefiles. The Census Bureau offers representatives of the 12 nonprofit ANRCs in Alaska the opportunity to review and update the ANRC boundaries before each decennial census.

Each ANRC is assigned a five-digit numeric Federal Information Processing Series (FIPS) code and an eight-digit National Standard (ANSI) code.

American Indian reservations-Federal (federal AIRs) are areas that have been set aside by the United States for the use of tribes, the exterior boundaries of which are more particularly defined in the final tribal treaties, agreements, executive orders, federal statutes, secretarial orders, or judicial determinations. The Bureau of Indian Affairs maintains a list of all federally recognized tribal governments and makes final determination of the inventory of federal AIRs. The Census Bureau recognizes federal reservations (and associated off-reservation trust lands) as territory over which American Indian tribes have primary governmental authority. American Indian reservations can be legally described as colonies, communities, Indian colonies, Indian communities, Indian rancherias, Indian reservations, Indian villages, pueblos, rancherias, ranches, reservations, reserves, settlements, or villages. The Census Bureau contacts representatives of American Indian tribal governments to identify the boundaries for federal reservations through its annual Boundary and Annexation Survey. Federal reservations may cross state and all other area boundaries.

Each federal AIR is assigned a four-digit census code ranging from 0001 through 4799 in alphabetical order of AIR names nationwide. This nation-based census code is the primary unique identifier for the AIR. Each federal AIR also is assigned a five-digit Federal Information Processing Series (FIPS) code and an eight-digit National Standard (ANSI) code. Because FIPS codes are assigned in alphabetical sequence within each state, the FIPS code will be different in each state for reservations that include territory in more than one state.
American Indian reservations-State (state AIRs) are reservations established by some state governments for tribes recognized by the state. A governor-appointed state liaison provides the names and boundaries for state-recognized American Indian reservations to the Census Bureau. State reservations must be defined within a single state but may cross county and other types of boundaries. Each state AIR is assigned a four-digit census code ranging from 9000 through 9499. Each state AIR also is assigned a five-digit Federal Information Processing Series (FIPS) code and an eight-digit National Standard (ANSI) code. To further identify and differentiate state-recognized American Indian areas from those that are federally recognized, the text (state) is appended to the AIR name.

American Indian tribal subdivisions, described as additions, administrative areas, areas, chapters, county districts, communities, districts, or segments, are legal administrative subdivisions of federally recognized American Indian reservations and off-reservation trust lands or are statistical subdivisions of Oklahoma tribal statistical areas (OTSAs). These entities are internal units of self-government or administration that serve social, cultural, and/or economic purposes for the American Indians on the reservations, off-reservation trust lands, or OTSAs. The Census Bureau obtains the boundary and name information for tribal subdivisions from tribal governments. Each American Indian tribal subdivision is assigned a three-digit census code that is alphabetically in order and unique within each American Indian area, a five-digit Federal Information Processing Series (FIPS) code assigned alphabetically within state, and an eight-digit National Standard (ANSI) code. Because FIPS codes are assigned in alphabetical sequence within each state, the FIPS code will be different in each state for tribal subdivisions that include territory in more than one state. All the summary levels that include tribal subdivisions in the presentation hierarchy will only have records for the 24 American Indian areas and two OTSAs that actually have tribal subdivisions. The list of areas and four-digit census codes is:
Code American Indian Area
0335 Bois Forte Reservation, MN
0605 Cheyenne River Reservation and Off-Reservation Trust Land, SD
0855 Crow Creek Reservation, SD
0990 Eastern Cherokee Reservation, NC
1110 Flathead Reservation, MT
1150 Fort Belknap Reservation and Off-Reservation Trust Land, MT
1160 Fort Berthold Reservation, ND
1250 Fort Peck Indian Reservation and Off-Reservation Trust Land, MT
1310 Gila River Indian Reservation, AZ
1505 Hopi Reservation and Off-Reservation Trust Land, AZ
1830 Lac Vieux Desert Reservation, MI
1860 Lake Traverse Reservation and Off-Reservation Trust Land, ND-SD
2175 Menominee Reservation, WI
2430 Navajo Nation Reservation and Off-Reservation Trust Land, AZ-NM-UT
2490 Northern Cheyenne Indian Reservation and Off-Reservation Trust Land, MT
2810 Pine Ridge Reservation, SD-NE
3100 Red Lake Reservation, MN
3235 Rosebud Indian Reservation and Off-Reservation Trust Land, SD
3340 Salt River Reservation, AZ
3680 Shakopee Mdewakanton Sioux Community, MN
3935 Spirit Lake Reservation, ND
3970 Standing Rock Reservation, SD-ND
4200 Tohono Oodham Nation Reservation and Off-Reservation Trust Land, AZ
4290 Tulalip Reservation and Off-Reservation Trust Land, WA
5550 Cherokee OTSA, OK
5590 Choctaw OTSA, OK


Hawaiian home lands (HHLs) are areas held in trust for Native Hawaiians by the state of Hawaii, pursuant to the Hawaiian Homes Commission Act of 1920, as amended. The Census Bureau obtains the names and boundaries for HHLs from state officials. The names of the home lands are based on the traditional ahupua' a names of the Crown and government lands of the Kingdom of Hawaii from which the lands were designated or from the local name for an area. Being lands held in trust, HHLs are treated as equivalent to off-reservation trust land areas with the American Indian Trust Land/Hawaiian Home Land Indicator coded as T. Each HHL is assigned a national four-digit census code ranging from 5000 through 5499 based on the alphabetical sequence of each HHL name, a five-digit Federal Information Processing Series (FIPS) code in alphabetical order within the state of Hawaii, and an eight-digit National Standard (ANSI) code.

Joint-use areas, as applied to any American Indian area by the Census Bureau, means an area that is administered jointly and/or claimed by two or more American Indian tribes. The Census Bureau designates legal joint-use areas as unique geographic entities equivalent to a reservation for the purpose of presenting statistical data. Each is assigned a national four-digit census code ranging from 4800 through 4999 based on the alphabetical sequence of each joint-use area name, a five-digit Federal Information Processing Series (FIPS) code in alphabetical order within state, and an eight-digit National Standard (ANSI) code. No joint-use areas exist in multiple states.

Off-reservation trust lands are areas for which the United States holds title in trust for the benefit of a tribe (tribal trust land) or for an individual American Indian (individual trust land). Trust lands can be alienated or encumbered only by the owner with the approval of the Secretary of the Interior or his/her authorized representative. Trust lands may be located on or off a reservation; however, the Census Bureau tabulates data only for off-reservation trust lands with the off-reservation trust lands always associated with a specific federally recognized reservation and/or tribal government. As for federally recognized reservations, the Census Bureau obtains the boundaries of off-reservation trust lands from American Indian tribal governments through its annual Boundary and Annexation Survey. The Census Bureau recognizes and tabulates data for reservations and off-reservation trust lands because American Indian tribes have primary governmental authority over these lands. The Census Bureau does not identify fee land (or land in fee simple status) or restricted fee lands as specific geographic areas.

Off-reservation trust lands are assigned a four-digit census code, a five-digit Federal Information Processing Series (FIPS) code, and an eight-digit National Standard (ANSI) code that is the same as that for the reservation with which they are associated. Trust lands associated with tribes that do not have a reservation are assigned unique codes. The census code is assigned by tribal name within the range 0001 through 4799, interspersed alphabetically among the reservation names. Because FIPS codes are assigned in alphabetical sequence within each state, the FIPS code will be different in each state for off-reservation trust lands that include territory in more than one state. In decennial census data tabulations, the American Indian Trust Land/Hawaiian Home Land Indicator uniquely identifies off-reservation trust lands, as well as reservation or statistical area only portions, Hawaiian home lands, and records that consist of the combination of reservation and off-reservation trust land territory.

Statistical Entities
Alaska Native village statistical areas (ANVSAs) represent the more densely settled portion of Alaska Native villages (ANVs). The ANVs constitute associations, bands, clans, communities, groups, tribes, or villages recognized pursuant to the Alaska Native Claims Settlement Act of 1971 (Public Law 92-203). Because ANVs do not have boundaries that are easy to locate, the Census Bureau does not delimit ANVs. Instead, the Census Bureau presents statistical data for ANVSAs that represent the settled portion of ANVs. In addition, each ANVSA should include only an area where Alaska Natives, especially members of the defining ANV, represent a substantial proportion of the population during at least one season of the year. ANVSAs are delineated or reviewed by officials of the ANV or, if no ANV official chose to participate in the delineation process, officials of the Alaska Native Regional Corporation (ANRC) in which the ANV is located. An ANVSA may not overlap the boundary of another ANVSA or an American Indian reservation. Each ANVSA is alphabetically assigned a national four-digit census code ranging from 6000 through 7999, an alphabetically assigned state-based five-digit Federal Information Processing Series (FIPS) code, and an eight-digit National Standard (ANSI) code.

Oklahoma tribal statistical areas (OTSAs) are statistical entities identified and delineated by the Census Bureau in consultation with federally recognized American Indian tribes that had a former reservation in Oklahoma. The boundary of an OTSA will be that of the former reservation in Oklahoma, except where modified by agreements with neighboring tribes for statistical data presentation purposes. Each OTSA is alphabetically assigned a national four-digit census code ranging from 5500 through 5899, an alphabetically assigned state-based five-digit Federal Information Processing Series (FIPS) code, and an eight-digit National Standard (ANSI) code. Tribal subdivisions are allowed within OTSAs and exist for the 2010 Census in the Cherokee and Choctaw OTSAs.

Oklahoma tribal statistical area (OTSA) Joint-Use Areas, as applied to OTSAs by the Census Bureau, means an area that is administered jointly and/or claimed by two or more American Indian tribes that have a delineated OTSA. The Census Bureau designates statistical joint-use areas as unique geographic entities for the purpose of presenting statistical data. Only Oklahoma tribal statistical areas have statistical joint-use areas. Each Oklahoma tribal joint-use area is alphabetically assigned a national four-digit census code ranging from 5900 through 5999, an alphabetically assigned state-based five-digit Federal Information Processing Series (FIPS) code, and an eight-digit National Standard (ANSI) code.

State designated tribal statistical areas (SDTSAs-referred to as State Designated American Indian Statistical Areas for Census 2000) are statistical entities for state-recognized American Indian tribes that do not have a state-recognized land base (reservation). SDTSAs are identified and delineated for the Census Bureau by a state liaison identified by the governors office in each state. SDTSAs generally encompass a compact and contiguous area that contains a concentration of people who identify with a state-recognized American Indian tribe and in which there is structured or organized tribal activity. An SDTSA may not be located in more than one state and it may not include area within any other American Indian, Alaska Native, or Native Hawaiian area. Each SDTSA is alphabetically assigned a four-digit census code ranging from 9500 through 9998, an alphabetically assigned state-based five-digit Federal Information Processing Series (FIPS) code, and an eight-digit National Standard (ANSI) code.

Tribal designated statistical areas (TDSAs) are statistical entities identified and delineated for the Census Bureau by federally recognized American Indian tribes that do not currently have a federally recognized land base (reservation or off-reservation trust land). A TDSA generally encompasses a compact and contiguous area that contains a concentration of individuals who identify with a federally recognized American Indian tribe and in which there is structured or organized tribal activity. A TDSA may be located in more than one state (although none do for 2010), but it may not include area within any other American Indian, Alaska Native, or Native Hawaiian area. Each TDSA is alphabetically assigned a four-digit census code ranging from 8000 through 8999, an alphabetically assigned state-based five-digit Federal Information Processing Series (FIPS) code, and an eight-digit National Standard (ANSI) code.

American Indian, Alaska Native, and Native Hawaiian Area (AIANNHA) Codes-AIANNHAs are represented in Census Bureau products using a national four-character numeric census code field and a single alphabetic character American Indian trust land/Hawaiian home land indicator field. The census codes are assigned in alphabetical order in assigned ranges by AIANNHA type nationwide, except that joint-use areas appear at the end of the code range. Off-reservation trust lands are assigned the same code as the reservation with which they are associated. Trust lands associated with tribes that do not have a reservation are assigned codes based on tribal name. Federal Information Processing Series (FIPS) codes for all AIANNHAs range from 00001 through 89999, without differentiation among the many types of areas.

The type of AIANNHA can be identified either by the census code or by the FIPS class code. The range of census codes allocated to each AIANNHA and the valid FIPS class code(s) associated with each are as follows:


AIANNHA type
Census code range
Valid FIPS class code(s)*
Federal American Indian reservation (AIR)/off-reservation trust land
0001 to 4799
D1, D2, D3, D5, D8
Hawaiian home land
5000 to 5499
F1
Oklahoma tribal statistical area (OTSA)
5500 to 5899
D6
Joint-use OTSA
5900 to 5999
D0
Alaska Native village statistical area (ANVSA)
6000 to 7999
E1
Tribal designated statistical area (TDSA)
8000 to 8999
D6
State AIR
9000 to 9499
D4
State designated tribal statistical area (SDTSA)
9500 to 9998
D9
AIANNHA type
American Indian, Alaska Native, Native Hawaiian area indicator
Hawaiian home land
T
American Indian reservation including associated off-reservation trust land
M
American Indian reservation or statistical entity only
R
Off-reservation trust land only
T

* Refer to the Data Dictionary for specific value descriptions.


Area Measurement
Area measurement data provide the size, in square units (metric and nonmetric) of geographic entities for which the Census Bureau tabulates and disseminates data. Area is calculated from the specific boundary recorded for each entity in the Census Bureaus geographic database. The Census Bureau provides area measurement data for both land area and water area. The water area figures include inland, coastal, Great Lakes, and territorial sea water. Inland water consists of any lake, reservoir, pond, or similar body of water that is recorded in the Census Bureaus geographic database. It also includes any river, creek, canal, stream, or similar feature that is recorded in that database as a two-dimensional feature (rather than as a single line). The portions of the oceans and related large embayments (such as Chesapeake Bay and Puget Sound), the Gulf of Mexico, and the Caribbean Sea that belong to the United States and its territories are classified as coastal and territorial waters; the Great Lakes are treated as a separate water entity. Rivers and bays that empty into these bodies of water are treated as inland water from the point beyond which they are narrower than 1 nautical mile across. Identification of land and inland, coastal, territorial, and Great Lakes waters is for data presentation purposes only and does not necessarily reflect their legal definitions.

Land and water area measurements may disagree with the information displayed on Census Bureau maps and in the MAF/TIGER database because, for area measurement purposes, hydrologic features identified as intermittent water, glacier, or swamp are reported as land area. The water area measurement reported for some geographic entities includes water that is not included in any lower-level geographic entity. Therefore, because water is contained only in a higher-level geographic entity, summing the water measurements for all the component lower-level geographic entities will not yield the water area of that higher-level entity. This occurs, for example, where water is associated with a county but is not within the legal boundary of any county subdivision. The accuracy of any area measurement data is limited by the accuracy inherent in 1) the location and shape of the various boundary information in the MAF/TIGER database, 2) the identification, and classification of water bodies coupled with the location and shapes of the shorelines of water bodies in that database, and 3) rounding affecting the last digit in all operations that compute and/or sum the area measurements.


Blocks (Census Blocks) are statistical areas bounded by visible features, such as streets, roads, streams, and railroad tracks, and by nonvisible boundaries, such as selected property lines and city, township, school district, and county limits and short line-of-sight extensions of streets and roads. Generally, census blocks are small in area; for example, a block in a city bounded on all sides by streets. Census blocks in suburban and rural areas may be large, irregular, and bounded by a variety of features, such as roads, streams, and transmission lines. In remote areas, census blocks may encompass hundreds of square miles. Census blocks cover the entire territory of the United States, Puerto Rico, and the Island Areas. Census blocks nest within all other tabulated census geographic entities and are the basis for all tabulated data.

Census Block Numbers-Census blocks are numbered uniquely with a four-digit census block number from 0000 to 9999 within census tract, which nest within state and county. The first digit of the census block number identifies the block group. Block numbers beginning with a zero (in Block Group 0) are only associated with water-only areas.

Block Group
Block Groups (BGs) are statistical divisions of census tracts, are generally defined to contain between 600 and 3,000 people, and are used to present data and control block numbering. A block group consists of clusters of blocks within the same census tract that have the same first digit of their four-digit census block number. For example, blocks 3001, 3002, 3003, . . ., 3999 in census tract 1210.02 belong to BG 3 in that census tract. Most BGs were delineated by local participants in the Census Bureaus Participant Statistical Areas Program. The Census Bureau delineated BGs only where a local or tribal government declined to participate, and a regional organization or State Data Center was not available to participate.

A BG usually covers a contiguous area. Each census tract contains at least one BG, and BGs are uniquely numbered within the census tract. Within the standard census geographic hierarchy, BGs never cross state, county, or census tract boundaries but may cross the boundaries of any other geographic entity. Tribal census tracts and tribal BGs are separate and unique geographic areas defined within federally recognized American Indian reservations and can cross state and county boundaries (see Tribal Census Tractand Tribal Block Group). The tribal census tracts and tribal block groups may be completely different from the census tracts and block groups defined by state and county.

Block Group Codes-BGs have a valid code range of 0 through 9. BGs beginning with a zero only contain water area and are generally in coastal and Great Lakes water and territorial seas, but also in larger inland water bodies. For the 2010 Census, a block group 0 for the water portion can be delineated in any census tract and not just those census tracts also defined to only include water area. This is a change from Census 2000, when block groups coded 0 only existed in census tracts with a code of 0. To differentiate between county-based block groups and tribal block groups, the codes for tribal block groups use an alphabetic character (see Tribal Block Group).

Boundary Changes
Many of the legal and statistical entities for which the Census Bureau tabulates decennial census data have had boundary changes between Census 2000 and the 2010 Census; that is, between January 1, 2000, and January 1, 2010. Boundary changes to legal entities result from:
  1. Annexations to or detachments from legally established governmental units.
  2. Mergers or consolidations of two or more governmental units.
  3. Establishment of new governmental units.
  4. Disincorporations or disorganizations of existing governmental units.
  5. Changes in treaties or executive orders and governmental action placing additional lands in trust.
  6. Decisions by federal, state, and local courts.
  7. Redistricting for congressional districts and state legislative districts.
  8. Ancillary changes to legal or statistical areas as a result of annexations and detachments; for example, reduction of territory for a census designated place as the result of an annexation by an adjacent incorporated place.
  9. Changes to correct errors or more accurately place boundaries relative to visible features.
  10. Changes to statistical areas as the result of concept or criteria changes.

All legal boundaries used for the 2010 Census are those reported to the Census Bureau to be in effect as of January 1, 2010. The statistical area boundaries also reflect a January 1, 2010, date for delineation. The legal boundaries are collected through various surveys and programs: the Boundary and Annexation Survey, Redistricting Data Program, and the School District Review Program. There is a Geographic Change User Note Indicator in data files that identifies entities for which there have been changes to boundaries or data attributes (for example, legal/statistical area description or code) between the two censuses.

Statistical entity boundaries generally are reviewed by local, state, or tribal governments and can have changes to adjust boundaries to visible features to better define the geographic area each encompasses or to account for shifts and changes in the population distribution within an area. Where statistical areas have a relationship to legal area boundaries, complementary updates occur; for example, removing territory from a census designated place if annexed to an incorporated place or contracting a tribal designated statistical area if the area is added to an American Indian reservation.

The historical counts shown for states, counties, county subdivisions, places, American Indian, Alaska Native, and Native Hawaiian areas, and other areas are not updated for boundary changes and thus, reflect the population and housing units in each entity as delineated at the time of each decennial census.


Census Division
Census Divisions are groupings of states and the District of Columbia that are subdivisions of the four census regions (see Census Region). There are nine census divisions, and each is identified by a single-digit census code. Puerto Rico and the Island Areas are not part of any census region or census division. For a list of all census regions, census divisions, and their constituent states, see Figure A-3.

Census Region
Census Regions are groupings of states and the District of Columbia that subdivide the United States for the presentation of census data. There are four census regions-Northeast, Midwest, South, and West. Each of the four census regions is divided into two or more census divisions (see Census Division). Each census region is identified by a single-digit census code. Puerto Rico and the Island Areas are not part of any census region or census division. For a list of all census regions, census divisions, and their constituent states, see Figure A-3.

Census Tract
Census Tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity that are updated by local participants prior to each decennial census as part of the Census Bureaus Participant Statistical Areas Program. The Census Bureau delineates census tracts in situations where no local participant existed or where state, local, or tribal governments declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of statistical data.

Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. A census tract usually covers a contiguous area; however, the spatial size of census tracts varies widely depending on the density of settlement. Census tract boundaries are delineated with the intention of being maintained over a long time so that statistical comparisons can be made from census to census. Census tracts occasionally are split due to population growth or merged as a result of substantial population decline.

Census tract boundaries generally follow visible and identifiable features. They may follow nonvisible legal boundaries, such as minor civil division (MCD) or incorporated place boundaries in some states and situations, to allow for census-tract-to-governmental-unit relationships where the governmental boundaries tend to remain unchanged between censuses. State and county boundaries always are census tract boundaries in the standard census geographic hierarchy. Tribal census tracts are a unique geographic entity defined within federally recognized American Indian reservations and off-reservation trust lands and can cross state and county boundaries. Tribal census tracts may be completely different from the census tracts and block groups defined by state and county (see Tribal Census Tract).

Census Tract Codes and Numbers-Census tracts are identified by an up to four-digit integer number and may have an optional two-digit suffix; for example 1457.02 or 23. The census tract codes consist of six digits with an implied decimal between the fourth and fifth digit corresponding to the basic census tract number but with leading zeroes and trailing zeroes for census tracts without a suffix. The tract number examples above would have codes of 145702 and 002300, respectively.

Some ranges of census tract numbers in the 2010 Census are used to identify distinctive types of census tracts. The code range in the 9400s is used for those census tracts with a majority of population, housing, or land area associated with an American Indian area and matches the numbering used in Census 2000. The code range in the 9800s is new for 2010 and is used to specifically identify special land-use census tracts; that is, census tracts defined to encompass a large area with little or no residential population with special characteristics, such as large parks or employment areas. The range of census tracts in the 9900s represents census tracts delineated specifically to cover large bodies of water. This is different from Census 2000 when water-only census tracts were assigned codes of all zeroes (000000); 000000 is no longer used as a census tract code for the 2010 Census.

The Census Bureau uses suffixes to help identify census tract changes for comparison purposes. Census tract suffixes may range from .01 to .98. As part of local review of existing census tracts before each census, some census tracts may have grown enough in population size to qualify as more than one census tract. When a census tract is split, the split parts usually retain the basic number but receive different suffixes. For example, if census tract 14 is split, the new tract numbers would be 14.01 and 14.02. In a few counties, local participants request major changes to, and renumbering of, the census tracts; however, this is generally discouraged. Changes to individual census tract boundaries usually do not result in census tract numbering changes.

Tribal Census Tracts in American Indian Areas-The Census Bureau introduced the concept of tribal census tracts for the first time for Census 2000. Tribal census tracts for that census consisted of the standard county-based census tracts tabulated within American Indian areas, thus allowing for the tracts to ignore state and county boundaries for tabulation. The Census Bureau assigned the 9400 range of numbers to identify specific tribal census tracts; however, not all tribal census tracts used this numbering scheme. For the 2010 Census, tribal census tracts no longer are tied to or numbered in the same way as the county-based census tracts (see Tribal Census Tract).

Codes for Geographic Entities
The Census Bureau and other federal agencies assign codes to geographic entities to facilitate the organization, presentation, and exchange of statistical data and other information. Geographic entity codes allow for the unambiguous identification of individual entities, generally within a specific, higher-level geographic entity (for example, county codes are assigned uniquely within each state). For geographic entities that have names (such as states, counties, places, county subdivisions, urban areas, and metropolitan and micropolitan statistical areas), codes generally are assigned alphabetically based on name.

Census Bureau data products contain several types of geographic entity codes: Federal Information Processing Series (FIPS), American National Standards Institute (ANSI), and Census Bureau codes.

Federal Information Processing Series (FIPS)-These are codes formerly known as Federal Information Processing Standards codes, until the National Institute of Standards and Technology (NIST) announced its decision in 2005 to remove geographic entity codes from its oversight. The Census Bureau continues to maintain and issue codes for geographic entities covered under FIPS oversight, albeit with a revised meaning for the FIPS acronym. Geographic entities covered under FIPS include states, counties, congressional districts, core based statistical areas, places, county subdivisions, subminor civil divisions, consolidated cities, and all types of American Indian, Alaska Native, and Native Hawaiian areas. FIPS codes are assigned alphabetically according to the name of the geographic entity and may change to maintain alphabetic sort when new entities are created or names change. FIPS codes for specific geographic entity types are usually unique within the next highest level of geographic entity with which a nesting relationship exists. For example, FIPS state, congressional district, and core based statistical area codes are unique within nation; FIPS county, place, county subdivision, and subminor civil division codes are unique within state. The codes for American Indian, Alaska Native, and Native Hawaiian areas also are unique within state; those areas in multiple states will have different codes for each state.

American National Standards Institute (ANSI)-With the removal of geographic entities from Federal Information Processing Standards oversight, the Census Bureau and other federal agencies have sought American National Standards Institute (ANSI) oversight authority for geographic entity codes. These codes are referred to as National Standard codes in some Census Bureau products. Geographic entities covered under ANSI include states, counties, congressional districts, core based statistical areas and related statistical areas, places, county subdivisions, consolidated cities, subminor civil divisions, and all types of American Indian, Alaska Native, and Native Hawaiian areas-Alaska Native regional corporations, Alaska Native village statistical areas, American Indian reservation and off-reservation trust lands, American Indian tribal subdivisions, Hawaiian home lands, Oklahoma tribal statistical areas, state designated tribal statistical areas, and tribal designated statistical areas.

Relationship between FIPS and ANSI codes-Geographic entities for which NIST formerly provided Federal Information Processing Standards oversight will continue to be referred to as FIPS (Federal Information Processing Series) codes in some Census Bureau data products, despite the Census Bureau having sought ANSI oversight authority. These geographic entities include states, counties, congressional districts, and core based statistical areas and related statistical areas. The Census Bureau continues to maintain and issue codes for these entities following the same structure and without change to existing codes, except when necessary to maintain alphabetic sorting based on names of entities. The Census Bureau also continues to maintain and issue five-digit FIPS codes (formerly FIPS 55) for places, county subdivisions, consolidated cities, subminor civil divisions, Alaska Native Regional Corporations, and all types of American Indian, Alaska Native, and Native Hawaiian areas but is not seeking ANSI oversight authority for these entity codes. The U.S. Geological Survey has ANSI oversight authority for its Geographic Names Information System identifier (GNIS ID), which has been adopted as a National Standard (NS) code for states, counties, places, county subdivisions, subminor civil divisions, consolidated cities, Alaska Native Regional Corporations, and all types of American Indian, Alaska Native, and Native Hawaiian areas. The Census Bureau will include the GNIS ID for these entities in its data products, portrayed as an eight-digit character numeric code and identified as ANSI. NS codes (GNIS IDs) will not sort geographic entities in alphabetical order based on name or title, as is the case with FIPS codes.

Census Bureau codes-The Census Bureau assigns and issues codes for a number of geographic entities for which FIPS or ANSI codes are not available, and sometimes in addition to FIPS and ANSI codes. Geographic entities for which census codes are assigned and issued in Census Bureau data products include regions, divisions, census tracts, block groups, census blocks, urban areas, and all types of American Indian, Alaska Native, and Native Hawaiian areas. Some codes-voting district, state legislative district, and school district-use standards established by the states-or for school districts, the U.S. Department of Education.

Congressional District
Congressional Districts are the 435 areas from which people are elected to the U.S. House of Representatives. After the apportionment of congressional seats among the states based on decennial census population counts, each state with multiple seats is responsible for establishing congressional districts for the purpose of electing representatives. Each congressional district is to be as equal in population to all other congressional districts in a state as practicable. For the District of Columbia, Puerto Rico, and each Island Area, a separate code is used to identify the entire areas of these state-equivalent entities as having a single nonvoting delegate.

Congressional District Codes-Congressional districts are identified by a two-character numeric Federal Information Processing Series (FIPS) code numbered uniquely within state. The District of Columbia, Puerto Rico, and the Island Areas have code 98 assigned identifying their nonvoting delegate status with respect to representation in Congress:

01 to 53 - Congressional district codes

00 - At large (single district for state)

98 - Nonvoting delegate

Consolidated City
Consolidated City-A consolidated government is a unit of local government for which the functions of an incorporated place and its county or minor civil division (MCD) have merged. This action results in both the primary incorporated place and the county or MCD continuing to exist as legal entities, even though the county or MCD performs few or no governmental functions and has few or no elected officials. Where this occurs-and where one or more other incorporated places in the county or MCD continue to function as separate governments, even though they have been included in the consolidated government-the primary incorporated place is referred to as a consolidated city. The Census Bureau classifies the

separately incorporated places within the consolidated city as place entities and creates a separate place (balance) record for the portion of the consolidated city not within any other place.
Consolidated City (Balance) Portions refer to the areas of a consolidated city not included in another separately incorporated place. For example, Butte-Silver Bow, MT, is a consolidated city (former Butte city and Silver Bow County) that includes the separately incorporated municipality of Walkerville city. The area of the consolidated city that is not in Walkerville city is assigned to Butte-Silver Bow (balance). The name always includes the (balance) identifier (see Place).

Core Based Statistical Areas and Related Statistical Areas
Core Based Statistical Areas (CBSAs) consist of the county or counties or equivalent entities associated with at least one core (urbanized area or urban cluster) of at least 10,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties with the counties associated with the core. The general concept of a CBSA is that of a core area containing a substantial population nucleus, together with adjacent communities having a high degree of economic and social integration with that core. The term core based statistical area became effective in 2003 and refers collectively to metropolitan statistical areas and micropolitan statistical areas. The U.S. Office of Management and Budget (OMB) defines CBSAs to provide a nationally consistent set of geographic entities for the United States and Puerto Rico for use in tabulating and presenting statistical data. Current CBSAs are based on application of the 2000 standards (published in the Federal Register of December 27, 2000) with Census 2000 data. The first set of areas defined based on the 2000 standards were announced on June 6, 2003; subsequent updates have been made to the universe of CBSAs and related statistical areas. No CBSAs are defined in the Island Areas. Statistical areas related to CBSAs include metropolitan divisions, combined statistical areas (CSAs), New England city and town areas (NECTAs), NECTA divisions, and combined NECTAs.

Combined New England City and Town Areas (Combined NECTAs) consist of two or more adjacent New England city and town areas (NECTAs) that have substantial employment interchange. The NECTAs that combine to create a combined NECTA retain separate identities within the larger combined NECTA. Because combined NECTAs represent groupings of NECTAs, they should not be ranked or compared with individual NECTAs.

Combined Statistical Areas (CSAs) consist of two or more adjacent CBSAs that have substantial employment interchange. The CBSAs that combine to create a CSA retain separate identities within the larger CSA. Because CSAs represent groupings of metropolitan and/or micropolitan statistical areas, they should not be ranked or compared with individual metropolitan and micropolitan statistical areas.

Metropolitan Divisions are smaller groupings of counties or equivalent entities defined within a metropolitan statistical area containing a single core with a population of at least 2.5 million. Not all metropolitan statistical areas with urbanized areas of this size will contain metropolitan divisions. A metropolitan division consists of one or more main/secondary counties that represent an employment center or centers, plus adjacent counties associated with the main/secondary county or counties through commuting ties. Because metropolitan divisions represent subdivisions of larger metropolitan statistical areas, it is not appropriate to rank or compare metropolitan divisions with metropolitan and micropolitan statistical areas. It would be appropriate to rank and compare metropolitan divisions.

Metropolitan Statistical Areas are CBSAs associated with at least one urbanized area that has a population of at least 50,000. The metropolitan statistical area comprises the central county or counties or equivalent entities containing the core, plus adjacent outlying counties having a high degree of social and economic integration with the central county or counties as measured through commuting.

Micropolitan Statistical Areas are CBSAs associated with at least one urban cluster that has a population of at least 10,000 but less than 50,000. The micropolitan statistical area comprises the central county or counties or equivalent entities containing the core, plus adjacent outlying counties having a high degree of social and economic integration with the central county or counties as measured through commuting.

New England City and Town Areas (NECTAs) are an alternative set of geographic entities, similar in concept to the county-based CBSAs defined nationwide, that OMB defines in New England based on county subdivisions-usually cities and towns. NECTAs are defined using the same criteria as county-based CBSAs, and, similar to CBSAs, NECTAs are categorized as metropolitan or micropolitan.

New England City and Town Area (NECTA) Divisions are smaller groupings of cities and towns defined within a NECTA containing a single core with a population of at least 2.5 million. A NECTA division consists of a main city or town that represents an employment center, plus adjacent cities and towns associated with the main city or town through commuting ties. Each NECTA division must contain a total population of 100,000 or more. Because NECTA divisions represent subdivisions of larger NECTAs, it is not appropriate to rank or compare NECTA divisions with NECTAs. It would be appropriate to rank and compare NECTA divisions.

Principal Cities of a CBSA (or NECTA) include the largest incorporated place with a population of at least 10,000 in the CBSA, or if no incorporated place of at least 10,000 population is present in the CBSA, the largest incorporated place or census designated place (CDP) in the CBSA. Principal cities also include any additional incorporated place or CDP with a population of at least 250,000 or in which 100,000 or more persons work; any additional incorporated place or CDP with a population of at least 50,000 and in which the number of jobs meets or exceeds the number of employed residents; and any additional incorporated place or CDP with a population of at least 10,000 but less than 50,000 and at least one-third the population size of the largest place and in which the number of jobs meets or exceeds the number of employed residents. Note that there are some places designated as principal cities of NECTAs that are not principal cities of a CBSA.

Core Based Statistical Area Codes-Metropolitan statistical areas, micropolitan statistical areas, NECTAs, metropolitan divisions, and NECTA divisions are identified using a five-digit numeric code that is assigned alphabetically based on title and is unique within the nation. The combined statistical area and combined NECTAs are identified using a three-digit numeric code, also assigned alphabetically based on title and unique within the nation. Codes, length, and ranges are:


CBSA entity
Length
Range*
Metropolitan statistical area.......................................... Five digits
10000−49999
Micropolitan statistical area.......................................... Five digits
10000−49999
Metropolitan division.................................................... Five digits
10004−49994
New England city and town area (NECTA)................... Five digits
70000−79999
NECTA division........................................................... Five digits
70004−79994
Combined statistical area............................................... Three digits
100−599
Combined NECTA...................................................... Three digits
700−799


* Metropolitan divisions and NECTA divisions are distinguished from metropolitan and micropolitan statistical areas and NECTAs by codes that end in "4." Metropolitan and micropolitan statistical areas and NECTAs cannot end in "4".


County or Statistically Equivalent Entity
The primary legal divisions of most states are termed counties. In Louisiana, these divisions are known as parishes. In Alaska, which has no counties, the equivalent entities are the organized boroughs, city and boroughs, municipalities, and census areas; the latter of which are delineated cooperatively for statistical purposes by the state of Alaska and the Census Bureau. In four states (Maryland, Missouri, Nevada, and Virginia), there are one or more incorporated places that are independent of any county organization and thus constitute primary divisions of their states. These incorporated places are known as independent cities and are treated as equivalent entities for purposes of data presentation. The District of Columbia and Guam have no primary divisions, and each area is considered an equivalent entity for purposes of data presentation. All of the counties in Connecticut and Rhode Island and nine counties in Massachusetts were dissolved as functioning governmental entities; however, the Census Bureau continues to present data for these historical entities in order to provide comparable geographic units at the county level of the geographic hierarchy for these states and represents them as nonfunctioning legal entities in data products. The Census Bureau treats the following entities as equivalents of counties for purposes of data presentation: municipios in Puerto Rico, districts and islands in American Samoa, municipalities in the Commonwealth of the Northern Mariana Islands, and islands in the U.S. Virgin Islands. Each county or statistically equivalent entity is assigned a three-character numeric Federal Information Processing Series (FIPS) code based on alphabetical sequence that is unique within state and an eight-digit National Standard feature identifier.

County Subdivision
County Subdivisions are the primary divisions of counties and equivalent entities. They include census county divisions, census subareas, minor civil divisions, and unorganized territories and can be classified as either legal or statistical. Each county subdivision is assigned a five-character numeric Federal Information Processing Series (FIPS) code based on alphabetical sequence within state and an eight-digit National Standard feature identifier.

Legal Entities
Minor civil divisions (MCDs) are the primary governmental or administrative divisions of a county in many states (parishes in Louisiana) and the county equivalents in Puerto Rico and the Island Areas. MCDs in the United States, Puerto Rico, and the Island Areas represent many different kinds of legal entities with a wide variety of governmental and/or administrative functions. MCDs include areas variously designated as barrios, barrios-pueblo, boroughs, charter townships, commissioner districts, election districts, election precincts, gores, grants, locations, magisterial districts, parish governing authority districts, plantations, purchases, reservations, supervisors districts, towns, and townships. The Census Bureau recognizes MCDs in 29 states, Puerto Rico, and the Island Areas. The District of Columbia has no primary divisions and is considered equivalent to an MCD for statistical purposes. (It is also considered a state equivalent and a county equivalent.) The 29* states in which MCDs are recognized are:


Arkansas Michigan Ohio
Connecticut Minnesota Pennsylvania
Illinois Mississippi Rhode Island
Indiana Missouri South Dakota
Iowa Nebraska Tennessee
Kansas New Hampshire Vermont
Louisiana New Jersey Virginia
Maine New York West Virginia
Maryland North Carolina Wisconsin
Massachusetts North Dakota


* Tennessee, a state with statistical census county divisions (CCDs) in 2000, reverted to MCDs in 2008.
In some states, all or some incorporated places are not part of any MCD; these places are termed independent places. Independent places also serve as primary legal subdivisions and have a Federal Information Processing Series (FIPS) county subdivision code and National Standard (ANSI) code that is the same as the FIPS and ANSI place code. In nine states-Maine, Massachusetts, New Hampshire, New Jersey, North Dakota, Pennsylvania, Rhode Island, South Dakota, and Wisconsin-all incorporated places are independent places. In other states, incorporated places are part of, or dependent within, the MCDs in which they are located, or the pattern is mixed-some incorporated places are independent of MCDs and others are included within one or more MCDs.

The MCDs in 12 states (Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin) also serve as general-purpose local governments that can perform the same governmental functions as incorporated places. The Census Bureau presents data for these MCDs in all data products for which place data are provided.

In New York and Maine, American Indian reservations (AIRs) generally exist outside the jurisdiction of any town (MCD) and thus also serve as the equivalent of MCDs for purposes of data presentation.

In states with MCDs, the Census Bureau assigns a default FIPS county subdivision code of 00000 and ANSI code of eight zeroes in some coastal, territorial sea, and Great Lakes water where county subdivisions do not legally extend into the Great Lakes or out to the 3-mile limit.

Statistical Entities
Census county divisions (CCDs) are areas delineated by the Census Bureau in cooperation with state, tribal, and local officials for statistical purposes. CCDs have no legal function and are not governmental units. CCD boundaries usually follow visible features and usually coincide with census tract boundaries. The name of each CCD is based on a place, county, or well-known local name that identifies its location. CCDs exist where:
1. There are no legally established MCDs.
2. The legally established MCDs do not have governmental or administrative purposes.
3. The boundaries of the MCDs change frequently.
4. The MCDs are not generally known to the public.

Alabama Hawaii Oregon
Arizona Idaho South Carolina
California Kentucky Texas
Colorado Montana Utah
Delaware Nevada Washington
Florida New Mexico Wyoming
Georgia Oklahoma

* Tennessee, a CCD state in 2000, reverted to a MCD state in 2008.

Census subareas are statistical subdivisions of boroughs, city and boroughs, municipalities, and census areas, all of which are statistical equivalent entities for counties in Alaska. The state of Alaska and the Census Bureau cooperatively delineate the census subareas to serve as the statistical equivalents of MCDs.
Unorganized territories (UTs) are defined by the Census Bureau in nine MCD states where portions of counties or equivalent entities are not included in any legally established MCD or incorporated place. The Census Bureau recognizes such separate pieces of territory as one or more separate county subdivisions for census purposes. It assigns each unorganized territory a descriptive name, followed by the designation &quote;UT&quote; and a county subdivision FIPS and ANSI code. The following states have unorganized territories:





Arkansas Maine North Carolina
Indiana Minnesota North Dakota
Iowa New York South Dakota


Geographic Area Attributes
The Census Bureau collects and maintains information describing selected attributes and characteristics of geographic areas. These attributes are Federal Information Processing Series (FIPS) class code, functional status, legal/statistical area description, internal point, and name of geographic entities.

FIPS class codes describe the general characteristics of a geographic area related to its legal or statistical status, governmental status, and in some cases relationship to other geographic entities. Class codes exist for counties; county subdivisions; subminor civil divisions; places; consolidated cities; Alaska Native Regional Corporations; American Indian, Alaska Native, and Native Hawaiian areas; and American Indian tribal subdivisions.

Functional status describes whether a geographic entity is a functioning governmental unit, has an inactive government, is an administrative area without a functioning government, or is a statistical area identified and defined solely for tabulation and presentation of statistical data. Functional status codes are:


A - Active government providing primary general-purpose functions.
B - Active government that is partially consolidated with another government but with separate officials providing primary general-purpose functions.
C - Active government consolidated with another government with a single set of officials.
E - Active government providing special-purpose functions.
F - Fictitious entity created to fill the Census Bureaus geographic hierarchy.
G - Active government that is subordinate to another unit of government and thus, not considered a functioning government.
I - Inactive governmental unit that has the power to provide primary special-purpose functions.
N - Nonfunctioning legal entity.
S - Statistical entity.


Internal point-The Census Bureau calculates an internal point (latitude and longitude coordinates) for each geographic entity. For many geographic entities, the internal point is at or near the geographic center of the entity. For some irregularly shaped entities (such as those shaped like a crescent), the calculated geographic center may be located outside the boundaries of the entity. In such instances, the internal point is identified as a point inside the entity boundaries nearest to the calculated geographic center and, if possible, within a land polygon.

Legal/statistical area description (LSAD)-The LSAD describes the particular typology for each geographic entity; that is, whether the entity is a borough, city, county, town, or township, among others. For legal entities, the LSAD reflects the term that appears in legal documentation pertaining to the entity, such as a treaty, charter, legislation, resolution, or ordinance. For statistical entities, the LSAD is the term assigned by the Census Bureau or other agency defining the entity. The LSAD code is a two-character field that corresponds to a description of the legal or statistical type of entity and identifies whether the LSAD term should be capitalized and should precede or follow the name of the geographic entity. Note that the same LSAD code is assigned to entities at different levels of the geographic hierarchy when they share the same LSAD. For example, the Census Bureau assigns the same LSAD code (21) to boroughs in New York and Connecticut, although they are county subdivisions in the former and incorporated places in the latter.

Name-Each geographic entity included in Census Bureau products has a name. For most geographic entities, the name is derived from the official legally recognized name, is assigned by local officials participating in Census Bureau statistical area programs, or is based on component entities and determined according to specified criteria. For legal entities, the name appearing in Census Bureau products may be the more commonly used name rather than the name as it appears in legal documents. For example, Virginia instead of the Commonwealth of Virginia; Baltimore instead of City of Baltimore. In some instances, the name for an entity in Census Bureau products will reflect the official name as well as a more commonly used name listed parenthetically; i.e., San Buenaventura (Ventura), CA, or Bath (Berkeley Springs), WV. For some types of geographic entities, the name reflected in Census Bureau products may be the geographic entity code assigned by local officials. For example, a census tracts name is the actual number assigned by local officials, such as 1.01, whereas the census tract code would reflect a full four-digit base code and two-digit suffix (for example, for the preceding tract named 1.01, 000101).

Geographic Names Information System
Geographic Names Information System (GNIS) is the federal standard for geographic nomenclature. The U.S. Geological Survey (USGS) developed the GNIS for the U.S. Board on Geographic Names as the official repository of domestic geographic names data; the official vehicle for geographic names use by all departments of the federal government; and the source for applying geographic names to federal electronic and printed products. The GNIS contains information about physical and cultural geographic features of all types in the United States and its territories, current and historical, but not including roads and highways. The database holds the federally recognized name of each feature and defines the feature location by state, county, USGS topographic map, and geographic coordinates. Other attributes include names or spellings other than the official name, feature designations, feature classification, historical and descriptive information, and, for some categories, the geometric boundaries.

Geographic Names Information System Identifier
The Geographic Names Information System Identifier (GNIS ID) is a variable length, permanent, numeric identifier of up to ten digits in length that identifies each entity uniquely within the nation. The GNIS is the new American National Standards Institute (ANSI) national standard code for several entity types. Because each entitys GNIS ID is permanent, it will not change if the entity changes its name or if creation of a new entity changes the alphabetic sort. (Federal Information Processing Series codes are assigned based on the alphabetic sorting of entity names within a state and occasionally require changing codes to maintain the alphabetic sort.) The GNIS IDs are assigned sequentially and stored in a right-justified, variable-length, numeric field without leading zeroes. The GNIS now contains more than 2.6 million sequential records, thus no GNIS ID currently exceeds seven digits. The Census Bureau portrays the GNIS ID in its data products as a fixed-width eight-character field with leading zeroes.

Island Areas of the United States
The Island Areas of the United States are American Samoa, Guam, the Commonwealth of the Northern Mariana Islands (Northern Mariana Islands), and the U.S. Virgin Islands.
The Census Bureau treats the Island Areas as entities that are statistically equivalent to states for data presentation purposes; data for the Island Areas, however, are presented separately from data for the United States and Puerto Rico. Geographic definitions specific to the Island Areas are shown in the appropriate publications and documentation that accompany the data products for the Island Areas. Sometimes the Island Areas are referred to as Island Territories or Insular Areas. For the 1990 and previous censuses, the U.S. Census Bureau referred to the entities as Outlying Areas.

Separate from the Island Areas is the term U.S. Minor Outlying Islands. The U.S. Minor Outlying Islands refers to certain small islands under U.S. jurisdiction in the Caribbean and Pacific: Baker Island, Howland Island, Jarvis Island, Johnston Atoll, Kingman Reef, Midway Islands, Navassa Island, Palmyra Atoll, and Wake Island. These areas usually are not part of standard data products.

Maf/Tiger Database
MAF/TIGER is an acronym for the Master Address File/Topologically Integrated Geographic Encoding and Referencing system or database. It is a digital (computer-readable) geographic database that automates the mapping and related geographic activities required to support the Census Bureaus census and survey programs. The Census Bureau developed the TIGER® system to automate the geographic support processes needed to meet the major geographic needs of the 1990 census: producing cartographic products to support data collection and map presentations, providing geographic structure for tabulation and dissemination of the collected statistical data, assigning residential and employer addresses to the correct geographic location and relating those locations to the geographic entities used for data tabulation, and so forth. During the 1990s, the Census Bureau developed an independent Master Address File (MAF) to support field operations and allocation of housing units for tabulations. After Census 2000, both the address-based MAF and geographic TIGER® databases merged to form MAF/TIGER. The content of the MAF/TIGER database is undergoing continuous updates and is made available to the public through a variety of TIGER/Line® shapefiles.


Incorporated Places are those reported to the Census Bureau as legally in existence as of January 1, 2010, as reported in the latest Boundary and Annexation Survey (BAS), under the laws of their respective states. An incorporated place is established to provide governmental functions for a concentration of people as opposed to a minor civil division, which generally is created to provide services or administer an area without regard, necessarily, to population. Places always are within a single state or equivalent entity, but may extend across county and county subdivision boundaries. An incorporated place usually is a city, town, village, or borough, but can have other legal descriptions. For Census Bureau data tabulation and presentation purposes, incorporated places exclude:

Boroughs in Alaska (treated as statistical equivalents of counties)

Towns in the New England states, New York, and Wisconsin (treated as MCDs)

Boroughs in New York (treated as MCDs)

Census Designated Places (CDPs) are the statistical counterparts of incorporated places, and are delineated to provide data for settled concentrations of population that are identifiable by name but are not legally incorporated under the laws of the state in which they are located. The boundaries usually are defined in cooperation with local or tribal officials and generally updated prior to each decennial census. These boundaries, which usually coincide with visible features or the boundary of an adjacent incorporated place or another legal entity boundary, have no legal status, nor do these places have officials elected to serve traditional municipal functions. CDP boundaries may change from one decennial census to the next with changes in the settlement pattern; a CDP with the same name as in an earlier census does not necessarily have the same boundary. CDPs must be contained within a single state and may not extend into an incorporated place. There are no population size requirements for CDPs.

Hawaii is the only state that has no incorporated places recognized by the Census Bureau. All places shown in decennial census data products for Hawaii are CDPs. By agreement with the state of Hawaii, the Census Bureau does not show data separately for the city of Honolulu, which is coextensive with Honolulu County. In Puerto Rico, which also does not have incorporated places, the Census Bureau recognizes only CDPs and refers to them as comunidades or zonas urbanas. Guam also has only CDPs.

Place Codes are of two types. The five-digit Federal Information Processing Series (FIPS) place code is assigned based on alphabetical sequence within a state. If place names are duplicated within a state and they represent distinctly different areas, a separate code is assigned to each place name alphabetically by the primary county in which each place is located, or if both places are in the same county, they are assigned alphabetically by their legal descriptions (for example, city before village). Places also are assigned an eight-digit National Standard (ANSI) code.

Dependent and Independent Places refers to the relationship of places to the county subdivisions. Depending on the state, incorporated places are either dependent within, or independent of, county subdivisions, or there is a mixture of dependent and independent places in the state and in a county. Dependent places are part of the county subdivision; the county subdivision code of the place is the same as that of the underlying county subdivision(s) but is different from the place code. Independent places are not part of any minor civil division (MCD) and serve as primary county subdivisions. The independent place FIPS code usually is the same as that used for the MCD for the place. The only exception is if the place is independent of the MCDs in a state (Iowa, Louisiana, Maryland, Nebraska, North Carolina, and Virginia) in which the FIPS MCD codes are in the 90000 range. Then, the FIPS MCD and FIPS place codes will differ. CDPs always are dependent within county subdivisions and all places are dependent within statistical county subdivisions.

Consolidated City (Balance) Portions refer to the areas of a consolidated city not included in another separately incorporated place. For example, Butte-Silver Bow, MT, is a consolidated city (former Butte city and Silver Bow County) that includes the separately incorporated municipality of Walkerville city. The area of the consolidated city that is not in Walkerville city is assigned to Butte-Silver Bow (balance). The name of the area of a consolidated city not specifically within a separately incorporated place always includes the (balance) identifier. Balance portions of consolidated cities are included with other places in Census Bureau products.

Population and Housing Unit Density
Population and housing unit density are computed by dividing the total population or number of housing units within a geographic entity by the land area of that entity measured in square miles or in square kilometers. Density is expressed as population per square mile (kilometer) or housing units per square mile (kilometer).

Public Use Microdata Areas
Public Use Microdata Areas (PUMAs) are geographic areas for which the Census Bureau provides selected extracts of raw data from a small sample of census records that are screened to protect confidentiality. These extracts are referred to as public use microdata sample (PUMS) files.

For the 2010 Census, each state, the District of Columbia, Puerto Rico, and some Island Area participants delineated PUMAs for use in presenting PUMS data based on a 5 percent sample of decennial census or American Community Survey data. These areas are required to contain at least 100,000 people. This is different from Census 2000 when two types of PUMAs were defined: a 5 percent PUMA as for 2010 and an additional super-PUMA designed to provide a 1 percent sample. The PUMAs are identified by a five-digit census code unique within state.

Puerto Rico
The Census Bureau treats the Commonwealth of Puerto Rico as the statistical equivalent of a state for data presentation purposes.

Municipio
The primary legal divisions of Puerto Rico are termed municipios. For data presentation purposes, the Census Bureau treats a municipio as the equivalent of a county in the United States.

Barrio, Barrio-Pueblo, and Subbarrio
The Census Bureau recognizes barrios and barrios-pueblo as the primary legal divisions of municipios. These entities are similar to the minor civil divisions (MCDs) used for reporting data in 29 states of the United States. Subbarrios in 23 municipios are the primary legal subdivisions of the barrios-pueblo and some barrios. The Census Bureau presents the same types of statistical data for these subminor civil divisions (sub-MCDs) as it does for the barrios and barrios-pueblo. (There is no geographic entity in the United States equivalent to the subbarrio.)

Zona Urbana and Comunidad
There are no incorporated places in Puerto Rico; instead, the Census Bureau provides data for two types of census designated places (CDPs): zonas urbanas, representing the governmental center of each municipio, and comunidades, representing other settlements. There are no minimum population size requirements for zonas urbanas and comunidades.
Some types of geographic entities do not apply in Puerto Rico. For instance, Puerto Rico is not in any census region or census division (see also Congressional District).


School Districts (Elementary, Secondary, and Unified )
School Districts are geographic entities within which state, county, local officials, the Bureau of Indian Affairs, or the U.S. Department of Defense provide public educational services for the areas residents. The Census Bureau obtains the boundaries, names, local education agency codes, and school district levels for school districts from state and local school officials for the primary purpose of providing the U.S. Department of Education with estimates of the number of children at risk within each school district, county, and state. This information serves as the basis for the Department of Education to determine the annual allocation of Title I funding to states and school districts.

The Census Bureau tabulates data for three types of school districts: elementary, secondary, and unified. Each school district is assigned a five-digit code that is unique within state. School district codes are the local education agency number assigned by the Department of Education and are not necessarily in alphabetical order by school district name.
The elementary school districts provide education to the lower grade/age levels and the secondary school districts provide education to the upper grade/age levels. Unified school districts provide education to children of all school ages in their service areas. In general, where there is a unified school district, no elementary or secondary school district exists; and where there is an elementary school district, the secondary school district may or may not exist.

The Census Bureaus representation of school districts in various data products is based both on the grade range that a school district operates and also the grade range for which the school district is financially responsible. For example, a school district is defined as an elementary school district if its operational grade range is less than the full kindergarten through 12 or prekindergarten through 12 grade range (for example, K-6 or pre-K-8). These elementary school districts do not provide direct educational services for grades 7-12, 9-12, or similar ranges. Some elementary school districts are financially responsible for the education of all school-aged children within their service areas and rely on other school districts to provide service for those grade ranges that are not operated by these elementary school districts. In these situations, in order to allocate all school-aged children to these school districts, the secondary school district code field is blank. For elementary school districts where the operational grade range and financially responsible grade range are the same, the secondary school district code field will contain a secondary school district code. There are no situations where an elementary school district does not exist and a secondary school district exists in Census Bureau records.

State or Statistically Equivalent Entity
States and Equivalent Entities are the primary governmental divisions of the United States. In addition to the 50 states, the Census Bureau treats the District of Columbia, Puerto Rico, American Samoa, the Commonwealth of the Northern Mariana Islands, Guam, and the U.S. Virgin Islands as the statistical equivalents of states for the purpose of data presentation.

State Legislative District (Upper nad Lower Chambers)
State Legislative Districts (SLDs) are the areas from which members are elected to state legislatures. The Census Bureau first reported data for SLDs as part of the 2000 Public Law (P.L.) 94-171 Redistricting Data File.

Current SLDs (2010 Election Cycle)-States participating in Phase 1 of the 2010 Census Redistricting Data Program voluntarily provided the Census Bureau with the 2006 election cycle boundaries, codes, and, in some cases, names for their SLDs. All 50 states, plus the District of Columbia and Puerto Rico, participated in Phase 1, State Legislative District Project (SLDP) of the 2010 CensusRedistricting Data Program. States subsequently provided legal changes to those plans through the Redistricting Data Office and/or corrections as part of Phase 2 of the 2010 Census Redistricting Data Program, as needed.

The SLDs embody the upper (senate-SLDU) and lower (house-SLDL) chambers of the state legislature. Nebraska has a unicameral legislature and the District of Columbia has a single council, both of which the Census Bureau treats as upper-chamber legislative areas for the purpose of data presentation. A unique three-character census code, identified by state participants, is assigned to each SLD within a state. In Connecticut, Hawaii, Illinois, Louisiana, Maine, Massachusetts, New Jersey, Ohio, and Puerto Rico, state officials did not define the SLDs to cover all of the state or state equivalent area (usually bodies of water). In these areas with no SLDs defined, the code ZZZ has been assigned, which is treated within state as a single SLD for purposes of data presentation. Maryland also has areas with no SLDs defined; in Maryland, these areas are coded with an initial Z by county or equivalent and treated as a unique SLD by county or equivalent. In Nebraska and the District of Columbia, the Census Bureau assigned the code 999 to represent a single SLDL where legally none exist.

SLD Names-The Census Bureau first reported names for SLDs as part of Phase 1 of the 2010 Census Redistricting Data Program. The SLD names with their translated legal/statistical area description are associated only with the current SLDs. Not all states provided names for their SLDs, therefore the code (or number) also serves as the name.

Tribal Block Group
The 2010 tribal block group concept and criteria are completely different from those used in 2000. For the Census 2000, tribal block groups were the standard state-county-census tract-block group areas retabulated under an American Indian area hierarchy; that is, American Indian area-tribal census tract-tribal block group. Tribal block groups only were applicable to legal federally recognized American Indian reservation and off-reservation trust land areas. Tribal block groups were defined to provide statistically significant sample data for small areas within American Indian areas, particularly those American Indian areas that crossed state or county boundaries where these boundaries were not meaningful for statistical purposes. The 2000 tribal block groups used the block group numbers and comprised all blocks beginning with a single number.

The 2010 tribal block groups are defined independently of the standard county-based block group delineation. For federally recognized American Indian tribes with reservations or off-reservation trust land and a population less than 1,200, a single tribal block group is defined. Tribal participants in qualifying areas with a population greater than 1,200 could define additional block groups within their reservation and/or off-reservation trust land without regard to the standard block group configuration.

Tribal block groups will contain blocks beginning with the same number as the standard county-based block group and could contain seemingly duplicate block numbers. To better identify and differentiate tribal block groups from county-based block groups, tribal block groups use the letter range A through K (except I, which could be confused with a number 1) to identify and code the tribal block group. Tribal block groups nest within tribal census tract.

Tribal Census Tract
The 2010 tribal census tract concept and criteria are completely different from those used in 2000. Tribal census tracts (also known as tribal tracts) in 2000 were the standard state-county-census tract areas retabulated under an American Indian area hierarchy; that is, American Indian area-tribal census tract. Federally recognized tribes with a reservation or off-reservation trust land delineated tribal census tracts working with local census tract participants to produce a single census tract plan. Tribal census tracts were designed to be permanent statistical divisions of American Indian areas for the presentation of comparable data between censuses, particularly for those American Indian areas that crossed state or county boundaries where these boundaries were not meaningful for statistical purposes.

For 2010, tribal census tracts are defined independently of the standard county-based tract delineation. For federally recognized American Indian tribes with reservations or off-reservation trust land and a population less than 2,400, a single tribal census tract is defined. Qualifying areas with a population greater than 2,400 could define additional tribal census tracts within their area.

In 2000, the tract number range of 9400 through 9499 was reserved for tribal census tracts and was required for those tribal census tracts that crossed state or county boundaries. Not all tribal census tracts in 2000, however, used this range. For 2010, tribal census tract codes will be six characters long with a leading T alphabetic character followed by five numeric codes having an implied decimal between the fourth and fifth character; for example, T01000, which translates as tribal census tract 10. Tribal block groups will nest within tribal census tract. Since individual blocks are defined within the standard state-county-census tract hierarchy, a tribal census tract can contain seemingly duplicate block numbers, thus tribal census tracts cannot be used to uniquely identify census blocks.

United States
The United States consists of the 50 states and the District of Columbia.

Urban and Rural
For the 2010 Census, the Census Bureau classified as urban all territory, population, and housing units located within urbanized areas (UAs) and urban clusters (UCs), both defined using the same criteria. The Census Bureau delineates UA and UC boundaries that represent densely developed territory, encompassing residential, commercial, and other nonresidential urban land uses. In general, this territory consists of areas of high population density and urban land use resulting in a representation of the urban footprint. Rural consists of all territory, population, and housing units located outside UAs and UCs.

For the 2010 Census, the urban and rural classification was applied to the 50 states, the District of Columbia, Puerto Rico, American Samoa, Guam, the Commonwealth of the Northern Mariana Islands, and the U.S. Virgin Islands.

Urbanized Areas (UAs)-An urbanized area consists of densely developed territory that contains 50,000 or more people. The Census Bureau delineates UAs to provide a better separation of urban and rural territory, population, and housing in the vicinity of large places.

Urban Clusters (UCs)-An urban cluster consists of densely developed territory that has at least 2,500 people but fewer than 50,000 people. The Census Bureau first introduced the UC concept for Census 2000 to provide a more consistent and accurate measure of urban population, housing, and territory throughout the United States, Puerto Rico, and the Island Areas.

Urban Area Titles and Codes-The title of each UA and UC may contain up to three incorporated place or census designated place (CDP) names and will include the two-letter U.S. Postal Service abbreviation for each state or statistically equivalent entity into which the UA or UC extends. However, if the UA or UC does not contain an incorporated place or CDP, the urban area title will include the single name of a minor civil division or populated place recognized by the U.S. Geological Surveys Geographic Names Information System.
Each UC and UA is assigned a five-digit numeric census code based on a national alphabetical sequence of all urban area names. A separate flag is included in data tabulation files to differentiate between UAs and UCs. In printed reports, this differentiation is included in the name.

Central Place-The 2010 Census urban areas will no longer include one or more designated central places. In preceding censuses, the central place included all incorporated or census designated places included in the urban area title, plus additional incorporated areas that met a population size criterion. The concept of central place for urban areas no longer is being applied.

Relationship to Other Geographic Entities-Geographic entities, such as metropolitan areas, counties, minor civil divisions, places, and census tracts, often contain both urban and rural territory, population, and housing units.

Urban Growth Areas
Urban Growth Areas (UGAs) are legally defined entities in Oregon and Washington that the Census Bureau includes in the MAF/TIGER database in agreement with the states. UGAs, which are defined around incorporated places, are used to regulate urban growth. UGA boundaries, which need not follow visible features, are delineated cooperatively by state and local officials and then confirmed in state law. UGAs are a pilot project first defined only in Oregon for Census 2000. Each UGA is identified by a five-digit numeric census code, usually the same as the five-digit Federal Information Processing Series (FIPS) code associated with the incorporated place for which the UGA is named.

Voting Districts
Voting Districts (VTDs) refer to the generic name for geographic entities, such as precincts, wards, and election districts, established by state governments for the purpose of conducting elections. States voluntarily participating in Phase 2 of the 2010 Census Redistricting Data Program provided the Census Bureau with boundaries, codes, and names for their VTDs. Each VTD is identified by a one-to-six-character alphanumeric census code that is unique within county. The code ZZZZZZ identifies a portion of counties (usually bodies of water) for which no VTDs were identified. For the 2010 Census, only Rhode Island did not participate in Phase 2 (the Voting District/Block Boundary Suggestion Project) of the 2010 Census Redistricting Data Program. Kentucky chose not to provide VTDs as part of their participation in Phase 2, and the states of Montana and Oregon provided VTDs for some counties. Therefore, for 2010 Census data products, no VTDs exist in select counties in Montana and Oregon or for the states of Rhode Island and Kentucky in their entirety. Participating states often submitted VTDs conforming to the feature network in the MAF/TIGER database rather than the complete legal boundary of the VTD. If requested by the participating state, the Census Bureau identified the VTDs that represent an actual voting district with an A in the voting district indicator field. Where a participating state indicated that the VTD has been modified to follow existing features, the VTD is a pseudo-VTD, and the voting district indicator contains P.

Zip Code Tabulation Areas
ZIP Code Tabulation Areas (ZCTAs) are approximate area representations of U.S. Postal Service (USPS) five-digit ZIP Code service areas that the Census Bureau creates using whole blocks to present statistical data from censuses and surveys. The Census Bureau defines ZCTAs by allocating each block that contains addresses to a single ZCTA, usually to the ZCTA that reflects the most frequently occurring ZIP Code for the addresses within that tabulation block. Blocks that do not contain addresses but are completely surrounded by a single ZCTA (enclaves) are assigned to the surrounding ZCTA; those surrounded by multiple ZCTAs will be added to a single ZCTA based on limited buffering performed between multiple ZCTAs. The Census Bureau identifies five-digit ZCTAs using a five-character numeric code that represents the most frequently occurring USPS ZIP Code within that ZCTA, and this code may contain leading zeros. There are significant changes to the 2010 ZCTA delineation from that used in 2000. Coverage was extended to include the Island Areas for 2010 so that the United States, Puerto Rico, and the Island Areas have ZCTAs. Unlike 2000, when areas that could not be assigned to a ZCTA were given a generic code ending in XX (land area) or HH (water area), for 2010 there is no universal coverage by ZCTAs, and only legitimate five-digit areas are defined. The 2010 ZCTAs will better represent the actual Zip Code service areas because the Census Bureau initiated a process before creation of 2010 blocks to add block boundaries that split polygons with large numbers of addresses using different Zip Codes. Data users should not use ZCTAs to identify the official USPS ZIP Code for mail delivery. The USPS makes periodic changes to ZIP Codes to support more efficient mail delivery. The ZCTAs process used primarily residential addresses and was biased towards Zip Codes used for city-style mail delivery, thus there may be Zip Codes that are primarily nonresidential or boxes only that may not have a corresponding ZCTA.







Census Regions, Census Divisions, and Their Constituent States

Northeast Region

New England Division:Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut
Middle Atlantic Division:New York, New Jersey, Pennsylvania

Midwest Region

East North Central Division:Ohio, Indiana, Illinois, Michigan, Wisconsin
West North Central Division:Minnesota, Iowa, Missouri, North Dakota, South Dakota, Nebraska, Kansas

South Region

South Atlantic Division:Delaware, Maryland, District of Columbia, Virginia, West Virginia, North Carolina, South Carolina,Georgia, Florida
East South Central Division:Kentucky, Tennessee, Alabama, Mississippi
West South Central Division:Arkansas, Louisiana, Oklahoma, Texas

West Region

Mountain Division:Montana, Idaho, Wyoming, Colorado, New Mexico, Arizona, Utah, Nevada
Pacific Division:Washington, Oregon, California, Alaska, Hawaii