United States: 1970, 1980, 1990

All households.

METROUS identifies the household's metropolitan area within the United States. Metropolitan areas are counties or combinations of counties centering on a substantial urban area. METROUS identifies the household's metropolitan area of enumeration if the household was located in a metropolitan area large enough to meet confidentiality requirements.

Despite the terminological and technical issues that follow, the concept of "metropolitan area" has remained essentially the same throughout the years. However, there are three basic comparability issues that all users should be aware of:

Most metropolitan areas encompassed less territory during earlier years than they did in later ones, as the census reconsidered and adjusted the boundaries of each metropolitan area to account for growth during each ten-year period.

As population grows and people migrate to urban areas, new metropolitan areas regularly emerge, so the number of them has steadily increased since the concept was first invented.

There were slight variations in how the concept was defined from census to census. The special notes on each year (below) offer an overview of how the metropolitan concept has changed over time.

Metropolitan areas have been referred to by different names over the years. In 1970 and 1980, the term was Standard Metropolitan Statistical Area (SMSA). In 1990 it was Metropolitan Area (MA), which included: free-standing Metropolitan Statistical Areas (MSAs) and, Consolidated Metropolitan Statistical Areas (CMSAs) consisting of two or more economically and socially linked metropolitan areas, called Primary Metropolitan Statistical Areas (PMSAs). Many PMSAs were separate SMSAs or SMAs before 1990.

Despite the terminological shifts, the general concept is the same for all years: A metropolitan area is an area consisting of a large population center and adjacent communities (usually counties) that have a high degree of economic and social interaction with that center. Metropolitan areas often cross state lines. Some Metropolitan areas contain more than one central city. In previous years, those cities may either have been the central cities of separate metropolitan areas or not part of any metropolitan areas.

In IPUMS-International, metropolitan areas are listed according to their 1990 definition. Because of changes in the county composition of metropolitan areas over time, however, the 1990 coding system had to be modified somewhat. In general, metropolitan areas that are part of a CMSA in 1990 are listed independently of the CMSA.

1950

The concept of Standard Metropolitan Area (SMA) was introduced in 1950. An SMA is a county or group of contiguous counties which contained at least one city of 50,000+ residents. To be part of an SMA, a county either had to contain the 50,000+ city, or had to be metropolitan in character and integrated with a central city.

1. To be considered metropolitan in character, a county had to

a. either contain 10,000 nonagricultural workers, or 10% of the nonagricultural workers working in the SMA, or contain 50+% of its population in minor civil divisions with a population density of 150+/square mile and contiguous with the central city, and b. have at least 2/3 of its employed residents working in nonagricultural occupations.

2. Criteria for integration with a central city include situations where:

a. 15+% of the workers residing in the county worked in the county which contained the SMA's largest city, or

b. 25+% of the workers employed in the county lived in the county which contained the SMA's largest city, or

c. the monthly total of phone calls from the county to the county which contained the SMA's largest city was 4+ times as large as the county's number of phone subscribers.

1960

No geographical units smaller than states were identified in the 1960 sample.

1970

1970 SMSAs were essentially the same as what were previously called SMAs, although in some cases there was no single central city of 50,000+ residents, but instead two or more contiguous cities of 15,000+ residents each with a combined population of 50,000+. If adjacent counties each had a city of 50,000+ residents, and the cities were within 20 miles of one another, they were placed within the same SMSA unless there was clear evidence that they should be separated.

To be part of an SMSA, then, a county either had to contain the central city (or cities), or, as in 1950, be considered metropolitan and integrated with the central city (or cities).

To be metropolitan, a county had to:

either contain 10,000 nonagricultural workers, or employ 10,000 nonagricultural workers, or contain at least one-tenth as many nonagricultural workers as the SMSA county with the largest city contained, or employ at least one-tenth as many nonagricultural workers as the SMSA county with the largest city employed, or contain 50+% of its population in minor civil divisions with a population density of 150+/square mile and contiguous with a central city, and, have a labor force that was at least 75% nonagricultural.

For a county to be considered integrated with the central city:

15+% of the workers residing in the county had to work in the county/counties containing the SMSA's central city/cities, or

25+% of the workers employed in the county had to live in the county/counties containing the SMSA's central city/cities.

B. Like 1950 SMAs, 1970 New England SMSAs follow town and city (not county) boundaries. Furthermore, the 1970 census used a different criterion for metropolitan character in New England than the one used for the rest of the country; a town or city was considered metropolitan in New England if its population density was 100+/square mile.

C. Due to confidentiality requirements, SMSAs are identified only if they contained 250,000+ residents in 1970.

1980

The 1980 SMSA definition is essentially the same as that for 1970, although one 1980 SMSA (Nassau-Suffolk, NY) had no proper central city. SMSAs with fewer than 100,000 residents are not identified for confidentiality reasons. The 1980 sample identifies all 282 qualifying SMSAs and codes the 36 remaining SMSAs into 18 SMSA pairs, each with a combined population of 100,000+. The pairing allows all metropolitan territory to be identified without violating confidentiality requirements. Each pair shares the code of the first SMSA in the listing below:

Bangor, ME and Lewiston-Auburn, ME

Tioga County, NY (part of the Binghampton, NY/PA SMSA) and Elmira, NY

Bismark, ND and Grand Forks, ND/MN

Bloomington, IN and Owensboro, KY

Bristol, CT and Meriden, CT

Bryan-College Station, TX and Sherman-Dennison, TX

Guilford County, NC (excluding Greensboro city and High Point city; the entire county is part of the Greensboro-Winston-Salem-High Point, NC SMSA) and Burlington, NC

Casper, WY and Great Falls, MT

Dubuque, IA and Iowa City, IA

El Paso, TX (excluding El Paso city) and Las Cruces, NM

Lawton, OK and Enid, OK

Fitchburg-Leominster, MA and Pittsfield, MA

Fort Walton Beach, FL and Panama City, FL

La Crosse, WI and Rochester, MN

Laredo, TX and Victoria, TX

Topeka, KS (excluding Topeka City) and Lawrence, KS

Saline County, AR (part of Little Rock-N. Little Rock, AR SMSA) and Pine Bluff, AR

Midland, TX and San Angelo, TX

1990

What were called SMSAs in 1970 and 1980 were referred to as "MAs" - Metropolitan Areas - in 1990. The definition in 1990 was virtually the same as in 1970 and 1980. Conceptually, the 1990 MAs are further divided into:

Free-standing Metropolitan Statistical Areas (MSAs), which are generally surrounded by nonmetropolitan territory and therefore not integrated with other metropolitan areas, and

Primary Metropolitan Statistical Areas (PMSAs), which are the same as MSAs except that they are near, and economically/socially linked to, other PMSAs to form larger "CMSAs" - Consolidated Metropolitan Statistical Areas.