The data on residence in 1985 were derived from answers to question 14b, which asked for the State (or foreign country), county, and place of residence on April 1, 1985, for those persons reporting in question 14a that on that date they lived in a different house than their current residence. Residence in 1985 is used in conjunction with location of current residence to determine the extent of residential mobility of the population and the resulting redistribution of the population across the various States, metropolitan areas, and regions of the country.

When no information on residence in 1985 was reported for a person, information for other family members, if available, was used to assign a location of residence in 1985. All cases of nonresponse or incomplete response that were not assigned a previous residence based on information from other family members were allocated the previous residence of another person with similar characteristics who provided complete information.

The tabulation category, "Same house," includes all persons 5 years old and over who did not move during the 5 years as well as those who had moved but by 1990 had returned to their 1985 residence. The category, "Different house in the United States," includes persons who lived in the United States in 1985 but in a different house or apartment from the one they occupied on April 1, 1990. These movers are then further subdivided according to the type of move.

In most tabulations, movers are divided into three groups according to their 1985 residence: "Different house, same county," "Different county, same State," and "Different State." The last group may be further subdivided into region of residence in 1985. The category, "Abroad," includes those persons who were residing in a foreign country, Puerto Rico, or an outlying area of the U.S. in 1985, including members of the Armed Forces and their dependents. Some tabulations show movers who were residing in Puerto Rico or an outlying area in 1985 separately from those residing in other countries.

In tabulations for metropolitan areas, movers are categorized according to the metropolitan status of their current and previous residences, resulting in such groups as movers within an MSA/PMSA, movers between PMSA's, movers from nonmetropolitan areas to MSA/PMSA, and movers from central cities to the remainder of an MSA/PMSA. In some tabulations, these categories are further subdivided by size of MSA/PMSA, region of current or previous residence, or movers within or between central cities and the remainder of the same or a different MSA/PMSA.

The size categories used in some tabulations for both 1985 and 1990 residence refer to the populations of the MSA/PMSA on April 1, 1990; that is, at the end of the migration interval.

Some tabulations present data on inmigrants, outmigrants, and net migration. "Inmigrants" are generally defined as those persons who entered a specified area by crossing its boundary from some point outside the area. In some tabulations, movers from abroad are included in the number of inmigrants; in others, only movers within the United States are included.

"Outmigrants" are persons who depart from a specific area by crossing its boundary to a point outside it, but without leaving the United States. "Net migration" is calculated by subtracting the number of outmigrants from the number of inmigrants and, depending upon the particular tabulation, may or may not include movers from abroad.

The net migration for the area is net inmigration if the result was positive and net outmigration if the result was negative. In the tabulations, net outmigration is indicated by a minus sign (-).

Inmigrants and outmigrants for States include only those persons who did not live in the same State in 1985 and 1990; that is, they exclude persons who moved between counties within the same State. Thus, the sum of the inmigrants to (or outmigrants from) all counties in any State is greater than the number of inmigrants to (or outmigrants from) that State. However, in the case of net migration, the sum of the nets for all the counties within a State equal the net for the State. In the same fashion, the net migration for a division or region equals the sum of the nets for the States comprising that division or region, while the number of inmigrants and outmigrants for that division or region is less than the sum of the inmigrants or outmigrants for the individual States.

The number of persons who were living in a different house in 1985 is somewhat less than the total number of moves during the 5-year period. Some persons in the same house at the two dates had moved during the 5-year period but by the time of the census had returned to their 1985 residence. Other persons who were living in a different house had made one or more intermediate moves. For similar reasons, the number of persons living in a different county, MSA/PMSA, or State or moving between nonmetropolitan areas may be understated.

Metropolitan statistical areas (MSA's) are relatively freestanding MA's and are not closely associated with other MA's. These areas typically are surrounded by nonmetropolitan counties. Metropolitan Area Title and Code The title of an MSA contains the name of its largest central city, and up to two additional city names, provided that the additional places meet specified levels of population, employment, and commuting. Generally, a city with a population of 250,000 or more is in the title, regardless of other criteria.
The title of a PMSA may contain up to three place names, as determined above, or up to three county names, sequenced in order of population. A CMSA title also may include up to three names, the first of which generally is the most populous central city in the area. The second name may be the first city or county name in the most populous remaining PMSA; the third name may be the first city or county name in the next most populous PMSA. A regional designation may be substituted for the second and/or third names in a CMSA title if such a designation is supported by local opinion and is deemed to be unambiguous and suitable by the Office of Management and Budget.

The titles for all MA's also contain the name of each State in which the area is located. Each metropolitan area is assigned a four-digit FIPS code, in alphabetical order nationwide. If the fourth digit of the code is a "2," it identifies a CMSA. Additionally, there is a separate set of two-digit codes for CMSA's, also assigned alphabetically.

If an area that qualifies as an MA has more than one million persons, primary metropolitan statistical areas (PMSA's) may be defined within it. PMSA's consist of a large urbanized county or cluster of counties that demonstrates very strong internal economic and social links, in addition to close ties to other portions of the larger area. When PMSA's are established, the larger area of which they are component parts is designated a consolidated metropolitan statistical area (CMSA).