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Documentation: ACS 2009 (3-Year Estimates)
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Publisher: U.S. Census Bureau
Document: ACS 2009-3yr Summary File: Technical Documentation
Social Explorer; U.S. Census Bureau; American Community Survey 2007-2009 Summary File: Technical Documentation.
ACS 2009-3yr Summary File: Technical Documentation
Chapter 1. Introduction

1.1. The American Community Survey
The American Community Survey (ACS) is a household survey conducted by the U.S. Census Bureau with an annual sample size of about 3 million addresses. The ACS data provides communities with the current information they need to plan investments and services. Information from the survey generates data that help determine how more than $400 billion in federal and state funds are distributed annually. Each year the survey produces data that cover the periods of 1-year, 3-year, and 5-year estimates for geographic areas in the United States and Puerto Rico, ranging from neighborhoods to Congressional districts to the entire nation. For more, information about the ACS, please visit

Most ACS tables are published on the Census Bureau's American FactFinder (AFF) website,, and are available for download in several forms. However, for the 2005-2009 ACS 5-year data release, 295 Detailed Tables and tables for census block groups are not published on American FactFinder. These tables can only be accessed by using the ACS Summary File. This document will brief data users on the contents of the ACS Summary File and explain how they can use it to obtain the 5-year estimates.

1.2. The American Community Survey Summary File
The American Community Survey Summary File (ACSSF) is a unique data product that includes all the estimates and margins of error from the Detailed Tables and geographies that are published for the ACS. Other ACS data products such as Subject Tables and Data Profiles are created from the Detailed Tables and are therefore not available in the Summary File.

Since the Detailed Tables contain over 18 billion cells, the tables are stored in a series of files with only the data from the tables, without such information as the title of the tables, the description of the rows, and the names of the geographic areas. That information is in other files that the user must merge with the data files to reproduce the tables.

The ACS Summary File data files are in American Standard Code for Information Interchange (ASCII) format. The files are divided into three types:
  • Geographies - (position based)
  • Estimates - (comma delimited)
  • Margins of Error - (comma delimited)
Chapter 2 discusses each component in detail and explains how to put them all together.

1.3. Topics and Geographies Covered
Data contained in the ACS Summary File cover demographic, social, economic, and housing subject areas. All Detailed Tables for the ACS 5-year estimates are in the Summary File and are listed in Appendix E. This appendix also shows whether a table is available for download on American FactFinder.

The published ACS Summary File geographies cover areas that are based on "summary levels". A summary level specifies the content and the hierarchical relationships of the geographic elements that are required to tabulate and summarize data. For example, summary level code "040" represents the U.S. States, Washington D.C., and Puerto Rico; while summary level code "050" represents counties and county equivalents within states. Many resources are available to help users understand the ACS geographic terms and concepts. For additional information, please visit

In addition to the ACS 1-year and 3-year summary levels, new summary levels are added to the 5-year data with expanded geographies including census tracts and block groups, and additional information for geographies such as American Indian areas, core based statistical areas, combined statistical areas, Congressional districts and state legislative districts. See the full list of summary levels published for the 5-year Detailed Tables in Appendix F. For the 2005-2009 ACS 5-year data release, data for census block groups are not published on American FactFinder and are only available using the ACS Summary File. The list of tables in Appendix E shows which tables are available at the block group level.

There are 295 Detailed Tables that are not available on American FactFinder, which are documented in Appendix E. All Detailed Tables, including those 295 tables, are available for download in comma-delimited format, which can be easily read into a spreadsheet, at The Data Profiles and Subject Tables are also available on this site.

1.4. Tools for Obtaining Data
Since using the ACS Summary File can be challenging, users should first check if their tables of interest are available for download on American FactFinder. (Up to 7,000 tables can be downloaded at one time using the American FactFinder Download Center.) Below are some other options to help users retrieve the tables they want. They are listed in order based on ease of use.

  • Summary File Excel Retrieval Tool
The Summary File Excel Retrieval Tool is a macro-driven Excel spreadsheet that provides a method to easily retrieve a table for the nation, states, and all of the geographic areas in a state (or for all cross-state geographic areas such as metropolitan statistical areas or census regions). This tool is designed to be easy to use, and does not require any programming experience. There is a drop down menu from which the user can select the state for the table and receive data for all geographies within the state. One key requirement is that Microsoft Excel 2007 or later is needed. Other hardware and software requirements for the tool are listed in Chapter 3.1. For more information about the application, see the ACS Summary File page at
  • Summary File Data Ferrett Tool (coming in January 2011)
DataFerrett is a tool provided by the Census Bureau to help users view, download, and manipulate a wide variety of data sets to suit their needs. Among the features provided by this tool is the ability to construct user-defined variables from the variables on the input data file(s), the ability for users to exclude data that is not of interest, a variety of options for downloading data, and the ability to create complex tabular reports from the data including graphs and thematic maps. The initial release of the 2005-2009 ACS Summary File data in DataFerrett, currently planned for January 2011, will focus primarily on the display and download capabilities of DataFerrett. This tool will be ideal for data users who wish to view, customize, and restrict the data that is downloaded from the 2005-2009 ACS Summary File. Detailed information about DataFerrett is not available in this document and will be available when the tool is released.

  • Summary File Excel Import Tool
The Summary File Excel Import Tool is a replicate of the Excel templates that Census 2000 provided for the SF3 summary file release. The Excel Import Tool provides a basic layout of each sequence in Excel in the same format as the estimate and margin of error files are formatted. For individuals that do not have Excel 2007 or later and are unable to use the Excel Retrieval Tool, the Excel Import Tool provides an alternative option to read the summary file into Excel. For more information on this tool, see Chapter 3.3.
  • SAS Programs
There are two programming options for SAS users. The first option is a set of individual SAS programs, one for each summary file by geography and sequence. These programs are best for users only interested in looking at a specific sequence for a specific geography. The second option is a single SAS program that is parameterized to allow users to read in any sequence for any geography into SAS. This program can also be used to read the entire summary file into SAS, and is designed for users looking for a large amount of data. For more information on these programs, see Chapter 3.1.

1.5. Notable Changes to the Summary File
For those who have previously used the ACS Summary File, the files for the 5-year estimates are basically the same with the following exceptions:

  • Geography Levels are Published Only on the Summary File
Census block group level data are available only from the Summary File and they are not available for download on American FactFinder. User tools that are available are covered in Chapter 3.

  • The "merge_5_6" File Has Been Renamed
The merge_5_6 file that links the tables to the sequence files they are in is now called the Sequence Number and Table Number Lookup file, a name that more accurately describes the purpose and contents of this file. Note that the sequence numbers are different for the 2005-2009 ACS 5-year Summary File than for other summary products including the 2009 ACS 1-year Summary File.

  • Folders Have Been Renamed
The names of the folders on the website that hold the zip files have been modified to better describe their contents. These have been renamed in an effort to deter novice users from inadvertently downloading the entire contents of the 2005-2009 ACS Summary File, which can take from 1 to 10 hours, depending on the speed of the Internet connection. (More information about download times can be found in Chapter 2.2.)
Folder Name for the 2009 1-Year Summary File Folder Name for the 2005-2009 5-Year Summary File
Entire_SF 2005-2009 ACSSF_All_In_Two_Giant_Files (Experienced Users Only)
Entire_States 2005-2009_ACSSF_By_State_All_Tables
Seq_by_ST 2005-2009_ACSSF_by_State_by_Sequence_Table_Subset

  • Summary File Format Has Been Modified
For convenience, the files in zip format in each directory are separated further by two types of zipped files: one for census tract and block group data and the other for all the remaining levels of geography. This file type is specified in the file name of each zip file. For more detail, see Chapter 2.2.

1.6. Contact Us
Please send any technical questions or comments on the ACS Summary File you have via email to: If you have questions or comments about the American Community Survey, you can submit a question online at