Metropolitan and Micropolitan Areas

Metropolitan and micropolitan statistical areas (metro and micro areas) are geographic entities defined by the U.S. Office of Management and Budget (OMB)—not the Census Bureau—for use by federal statistical agencies in collecting, tabulating, and publishing federal statistics.

The term core based statistical area (CBSA) is a collective term for both metro and micro areas.

A metropolitan area contains a core urban area of 50,000 or more population. 

A micropolitan area contains an urban core of at least 10,000, but less than 50,000, population.

The core urban area is not exactly the same thing as the incorporated city limits.  For example, both the City of Anniston and the City of Gadsden have less than 50,000 population, but Anniston and Gadsden are both legitimate OMB metro areas.

The terms consolidated metropolitan statistical area and primary metropolitan statistical area are now obsolete. Metropolitan division is generally equivalent to the now obsolete primary metropolitan statistical area. Be aware and be careful.

Each metro or micro area consists of one or more counties and includes the counties containing the core urban area, as well as any adjacent counties that have a high degree of social and economic integration, as measured by commuting to work, with the urban core.  That is, metro and micro areas are always drawn around county boundaries.

Stay alert!  OMB can, and does, add and subtract counties from metro and micro areas.  For example, over time Walker County has been in, then out, then back in the Birmingham metro area.

Metro and micro areas can cross state boundaries.  For example, Russell County, Alabama belongs to the Columbus, Georgia metro area.  Quitman County, Georgia belongs to the Eufaula, Alabama micro area.  The Auburn-Opelika metro area belongs to the Atlanta-Sandy Springs-Gainsville GA-AL combined statistical area.

A combined statistical area is a combination of adjacent metro-metro or metro-micro areas.  For example, the Mobile metro area (Mobile County alone) combines with the Daphne-Fairhope-Foley micro area (Baldwin County alone) to be the Mobile-Daphne-Fairhope combined area, which is the same geographic area as the pre-2000 Mobile MSA.  When areas are combined, they retain their separate designations as metropolitan or micropolitan statistical areas.  For example, Huntsville and Decatur are independent metro areas, but now they are also the Huntsville-Decatur combined area.

OMB also changes the names of metro and micro areas as circumstances warrant.  For example, the longtime Florence metro area is now the Florence-Muscle Shoals metro area. 

Guidance on Uses of Statistical Area Definitions
Metropolitan and micropolitan statistical area standards do not equate to an urban-rural classification.   Counties included in metropolitan and micropolitan statistical areas contain both urban and rural territory and populations.  Metro/micro definitions always follow county boundaries.  Urban/rural territory doesn’t respect those political borders.

OMB advises that all agencies collecting and publishing data for metropolitan, micropolitan, and combined statistical areas should use the most recent definitions of these areas. Frequent data users will realize that this doesn’t always happen the way it should.  Be careful when you are using guidelines, documents, applications, etc. that reference metro statistical areas.  You might have to figure out the difference between what used to be, what currently is, and what you are going to do about the difference.

OMB establishes and maintains the definitions of metropolitan, micropolitan, and combined statistical areas solely for statistical purposes. That is, OMB does not take into account any nonstatistical uses that may be made of the definitions, nor will OMB modify the definitions to meet the requirements of any nonstatistical program.

Thus, OMB cautions that metropolitan statistical area and micropolitan statistical area definitions should not be used to develop and implement federal, state, and local nonstatistical programs and policies. OMB says these areas are not intended to serve as a general-purpose geographic framework for nonstatistical activities, and they may or may not be suitable for use in program funding formulas.

Nevertheless, data users know that the metro and micro areas are used for nonstatistical activities such as program funding formulas.  When push comes to shove, OMB recognizes that some legislation specifies the use of metropolitan statistical areas for program purposes, including the allocation of federal funds, and they do work with Congress to clarify the foundations of these definitions and the resultant, often unintended consequences of their use for nonstatistical purposes.

Despite OMB’s best efforts, data users frequently find terminology in currently-enforced legislation that doesn’t match current realities.  For example, the term standard metropolitan statistical area or SMSA hasn’t been officially sanctioned since 1980, but we still occasionally see it in regulatory language we are working with in the 21st century.  Just because OMB made a change doesn’t mean every state and federal agency picked up on it and made the same change.  Data users need to be knowledgeable about the history of and current delineations of metro and micro statistical areas.

For explanations in greater depth and a list of current metro, micro, and combined areas, go to