Central County

The central county or counties of a metropolitan or micropolitan statistical area are those containing all or a substantial portion of the core urban area. These counties, in turn, are used in measuring commuting with other counties that potentially qualify for inclusion in the metropolitan or micropolitan statistical area as outlying counties.

Codes for Metropolitan Statistical Areas, Micropolitan Statistical Areas, and Related Statistical Areas

Codes for metropolitan and micropolitan statistical areas (collectively referred to as “Core Based Statistical Areas” or “CBSAs”) and metropolitan divisions are 5 digits in length. Codes for metropolitan and micropolitan statistical areas and metropolitan divisions fall within the 10000 to 49999 range and are assigned in alphabetical order by area title. Metropolitan divisions are distinguished by a 5-digit code ending in “4.” Combined statistical area codes are 3 digits in length. Combined statistical area codes fall within the 100 to 599 range.

Combined Statistical Area

Consists of two or more adjacent core based statistical areas (CBSAs) that have an employment interchange measure of 15 or more.

Core Based Statistical Areas (CBSAs)

Refer collectively to metropolitan statistical areas and micropolitan statistical areas. CBSAs consist of the county or counties (or equivalent entities) associated with at least one core (urban area) 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.

Employment Interchange Measure (EIM)

Is a measure of ties between two adjacent entities. It is the sum of the percentage of workers living in the smaller entity who work in the larger entity and the percentage of employment in the smaller entity that is accounted for by workers who reside in the larger entity.

Metropolitan Division

A county or group of counties (or equivalent entities) delineated within a larger metropolitan statistical area, provided that the larger metropolitan statistical area contains a single core with a population of at least 2.5 million and other criteria are met. 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. Not all metropolitan statistical areas will contain metropolitan divisions.

Metropolitan Statistical Area

A geographic entity delineated by the Office of Management and Budget for use by federal statistical agencies. Metropolitan statistical areas consist of the county or counties (or equivalent entities) associated with at least one urban area of at least 50,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties.

Metropolitan and micropolitan statistical areas are collectively referred to as "Core Based Statistical Areas" (CBSAs).

Micropolitan Statistical Area

A geographic entity delineated by the Office of Management and Budget for use by federal statistical agencies. Micropolitan statistical areas consist of the county or counties (or equivalent entities) associated with at least one urban area of at least 10,000 but less than 50,000 population, plus adjacent counties having a high degree of social and economic integration with the core as measured through commuting ties.

Metropolitan and micropolitan statistical areas are collectively referred to as "Core Based Statistical Areas" (CBSAs).

Outlying County

A county qualifies as outlying under the following circumstances: (1) one-quarter or more of the employed residents work in the central counties of the metropolitan or micropolitan statistical area, or (2) one-quarter or more of the employment is composed of workers who live in the central counties. Furthermore, outlying counties also include the counties of any smaller metropolitan or micropolitan statistical area that are adjacent to the metropolitan or micropolitan statistical area and merge with it.

Principal City

The largest incorporated place with a population of at least 10,000 in a core based statistical area (CBSA), or if no incorporated place of least 10,000 population is present in the CBSA, the largest incorporated place or census designated place (CDP) in the CBSA. Additional places that meet specific criteria are also identified as principal cities.