OMB’s Standards for Defining Metropolitan and Micropolitan Statistical Areas

OMB’s Standards for Defining Metropolitan and Micropolitan Statistical Areas

  • August 7th, 2019

OMB’s Standards for Defining
Metropolitan and Micropolitan Statistical Areas

Summary of the Notice in the Federal Register, December 27, 2000

The new standards replace and supersede the 1990 standards for defining Metropolitan Areas. These new standards will not affect the availability of federal data for states, counties, county subdivisions, and municipalities. The new standards apply only to defining metropolitan, and now micropolitan, areas.The new standards will consider statistical rules only when defining Metropolitan and Micropolitan Statistical Areas. Local opinion carries no weight, except in one instance detailed below.

Census 2000 data will be published using the old definitions. For the near term, the Census Bureau will tabulate and publish data from Census 2000 for all Metropolitan Areas in existence at the time of the census (that is, those areas defined as of April 1, 2000). OMB plans to announce new definitions of metropolitan and micropolitan areas based on the new standards and Census 2000 data in 2003. Federal agencies should begin to use the new area definitions to tabulate and publish statistics when the definitions are announced.

The new standards are not an urban-rural classification. The Metropolitan and Micropolitan Statistical Area Standards do not equate to an urban-rural classification. All counties included in Metropolitan and Micropolitan Statistical Areas and many other counties contain both urban and rural territory and populations. OMB recognizes that formal definitions of settlement types such as inner city, inner suburb, outer suburb, exurb, and rural are useful to researchers, analysts, and other users of federal data. However, such settlement types are not considered for the statistical areas in this classification.

Core Based Statistical Areas (CBSAs). Metropolitan and Micropolitan Statistical Areas will be called collectively Core Based Statistical Areas (CBSAs). Metropolitan Statistical Areas will be based on urbanized areas of 50,000 or more population and Micropolitan Statistical Areas will be based on urban clusters of at least 10,000 but less than 50,000 population. The location of these cores will be the basis for identifying the central counties of CBSAs. The use of urbanized areas as cores for Metropolitan Statistical Areas is consistent with current practice. Urban clusters, used to identify the Micropolitan Statistical Areas, will be identified by the Census Bureau following Census 2000 and will be conceptually similar to urbanized areas.

Counties will be the geographic building blocks. Counties will be the geographic building blocks for defining CBSAs throughout the United States and Puerto Rico. (Cities and towns will be the geographical building blocks for defining New England City and Town Areas (NECTAs).) Using counties as the building blocks continues the current practice.

Commuting patterns will determine how many counties are part of the CBSA. Journey to work, or commuting, will be the basis for grouping counties together to form CBSAs. A county qualifies as a CBSA county if (a) at least 25 percent of the employed residents of the county work in the CBSA’s central county or counties, or (b) at least 25 percent of the jobs in the potential outlying county are accounted for by workers who reside in the CBSA’s central county or counties. Measures of settlement structure, such as population density, will not qualify outlying counties for inclusion in CBSAs.

Some contiguous CBSAs will be merged to form a single CBSA. Contiguous CBSAs will be merged to form a single CBSA when the central county or counties of one area qualify as outlying to the central county of another. OMB will use the same minimum commuting threshold—25 percent—as is used to qualify outlying counties. Patterns of population distribution and commuting sometimes are complex and, as a result, close social and economic ties, as measured by commuting, exist between some contiguous CBSAs. Strong ties between the central counties of two contiguous CBSAs, similar to the ties between an outlying county and a central county, should be recognized by merging the two areas to form a single CBSA.

Some contiguous CBSAs can be combined. When ties between contiguous CBSAs are less intense than those captured by mergers, but still significant, those CBSAs can be combined. Combinations of CBSAs can occur with an employment interchange measure of at least 15 percent, but less than 25 percent, only if local opinion in both areas is in favor. Because a combination represents a relationship of moderate strength between two CBSAs, the combining areas will retain their identities as separate CBSAs within the combination.

Principal Cities will be used to title areas. The new rules ensure that at least one incorporated place of 10,000 or more population is recognized as a Principal City. The new rules also allow a fuller identification of places that represent the more important social and economic centers within a Metropolitan or Micropolitan Statistical Area. Under the previous recommendations, there were instances in which an incorporated place of at least 10,000 population accounted for a larger amount of employment than the most populous place, but lacked sufficient population to qualify as a Principal City. With the new emphasis on commuting patterns and place-of-work destinations, the new guidelines will recognize approximately 100 additional Principal Cities nationwide. There are four specific criteria for determining which places will be designated as Principal Cities. These criteria are found in Section 5 of the new standards.

Metropolitan Divisions can contain the names of up to three Principal Cities, in order of descending population size.

Local opinion. There is only one instance where local opinion plays any part in these standards, and that will be in the designation of and naming of Combined CBSAs. Where employment interchange measures at least 15 percent and less than 25 percent, the measured ties may be perceived as minimal by residents of the two areas. In these situations, local opinion is useful in determining whether to combine the two areas, and if so, what to name the combined area.

Current metropolitan areas will not be “grandfathered” in the implementation of the new standards. “Grandfathering” refers to the continued designation of an area even though it does not meet the standards currently in effect. To maintain the integrity of the classification, OMB will objectively apply the new standards rather than continuing to recognize areas that do not meet the standards. The current status of a county as being within or outside a Metropolitan Area will play no role in the application of the new standards.

New CBSAs will be defined and existing CBSAs will be redefined between censuses. The first areas to be designated using the new standards will be announced in 2003. In the years 2004 through 2007, OMB will designate new CBSAs if they meet certain qualifications, spelled out in the guidelines. It should be possible to use the Census Bureau’s American Community Survey in 2008 to update the definition of all existing CBSAs at that time.

For More Information

The “Standards for Defining Metropolitan and Micropolitan Statistical Areas Notice” appears in the Wednesday, December 27, 2000 Federal Register. Internet users can access the notice online by going to the Census Bureau’s web page at Under “Subjects A to Z” in the upper left-hand corner, click on the letter M, then scroll down to “Metropolitan Area Standards Review Project (MASRP).” There you can link either to a PDF version or an HTML version. The direct link to the PDF version is