Core Based Statistical Areas

Core Based Statistical Areas (CBSAs) is the collective term used to refer to metropolitan statistical areas and micropolitan statistical areas, which are delineated by the Office of Management and Budget (OMB). OMB generally defines a CBSA as an area that contains a central county that has a substantial urban population, along with any adjacent communities that have a high level of integration with the central county. In 2020, OMB defined CBSAs to consist of a county or multiple counties (or other equivalent entities) that contain a core urban area with a minimum population of 10,000.

Core urban areas may have adjacent outlying counties that have social and economic integration as measured through commuting ties. Outlying counties are defined based on residents who work in central counties of a CBSA or workers who live in the central county but work in the outlying county of a CBSA. A single CBSA may extend beyond a single state's borders.

The largest city in a CBSA is designated as a principal city. Additional cities may qualify if they meet certain population size and employment requirements.

Metropolitan statistical areas (MSAs) consist of a county or counties with a minimum of one urban area with a population of 50,000. Micropolitan statistical areas (µSAs) consist of a county or counties with a minimum of one urban area with a population of 10,000 and not exceeding 50,000. Some CBSAs include metropolitan divisions, which are defined as a county or group of counties that are delineated within a larger MSA that contains an urban core area with a minimum population of 2.5 million people.

OMB defines Combined Statistical Areas, which are made up of at least two adjacent CBSAs that have a defined degree of employment interchange. Additional criteria for these designations are provided by OMB, which establishes nationwide standards for CBSAs.

Delineations of CBSAs are different from the various urban and rural definitions used across the federal government. Rural areas can exist in counties that are part of either metropolitan statistical areas or micropolitan statistical areas, or they can exist in counties that fall outside of such areas.

OMB intends for the delineations of CBSAs to be used "solely for statistical purposes." The classification intends to provide "nationally consistent delineations for collecting, tabulating, and publishing Federal statistics for a set of geographic areas." In practice, though, CBSAs are used for nonstatistical purposes in some federal programs (such as the Centers for Medicare & Medicaid Services' hospital wage index). Federal agencies that use CBSAs for nonstatistical purposes do not make revisions to the OMB delineations. Nonstatistical uses of CBSAs have attracted congressional interest.

Figure 1 provides an example of CBSA delineations in New Hampshire based on OMB Bulletin No. 23-01 (discussed later in this product).

Figure 1. Core Based Statistical Areas Visualization CBSAs of New Hampshire using revised delineations published in OMB Bulletin No. 23-01

Source: 2023 TIGER/Line® Shapefiles: Core Based Statistical Areas, U.S. Census Bureau. Notes: Map produced by Molly Cox, Cartographer/Geospatial Analyst, Congressional Research Service. Some CBSAs in this map expand into neighboring states.

Revisions to CBSAs

Prior to CBSAs, the Bureau of the Budget (OMB's predecessor) established "standard metropolitan areas," which were first used in 1950 Census Bureau publications.

The standards for delineating CBSAs are considered to be Statistical Policy Directive (SPD) No. 7 issued by OMB. CBSA revisions are conducted following the decennial census. OMB delineates CBSAs using the most recent decennial census data along with commuting data collected from the American Community Survey (ACS), which is used to measure intercounty connectivity.

During the 2020 revision process, OMB requested public comment on the recommendation of raising the population threshold to qualify a metropolitan statistical area from 50,000 to 100,000. After significant public opposition, OMB decided to leave the 50,000 threshold in place.

The 2020 standards were published on July 16, 2021, and included a process for conducting updates to delineations over a 10-year period.

Annual Updates

These updates address qualification of new metropolitan and micropolitan statistical areas and are expected to impact fewer counties.

Five-Year ("Mid-Decade") Update

This broader update addresses issues such as qualification of various aspects of current CBSAs, titling of CBSAs, and potential merging of adjacent CBSAs.

Decennial Delineation

This is the initial redelineation following a decennial census and adoption of revised standards; it includes the changes in the mid-decade update and qualification of central counties.

Relevant Statute and Legislation

Title 44 Section 3504(e)(3) of the U.S. Code sets out OMB's responsibilities with respect to the federal statistical system.

In 2022, the Metropolitan Areas Protection (MAPS) Act was signed into law (P.L. 117-219). This law provides direction to OMB regarding revisions to CBSAs.

Notably, the MAPS Act changes Section 3504(e)(10) of Title 44 of the U.S. Code. Through the MAPS Act, OMB is required to ensure changes to CBSAs are

• accompanied by a public report that explains the scientific basis, criteria, and methodology behind the change and includes opinions from experts who were consulted on the change;
• not influenced by nonstatistical considerations, including program administration or service delivery; and
• not used to automatically initiate an update in domestic assistance programs that use the delineations for nonstatistical purposes; rather, agencies may apply an updated delineation through the notice-and-comment rulemaking process.

The MAPS Act also made changes to Sections 6102 and 6309 of Title 31 of the U.S. Code as it pertains to use of CBSAs in nonstatistical programs.

OMB Bulletin No. 23-01

In July 2023, OMB released Bulletin No. 23-01, which reflects the 2020 standards for delineating CBSAs. The bulletin establishes the delineations, provides guidance for their use, and contains a list of all CBSAs. The bulletin identifies

• 393 Metropolitan Statistical Areas, which contain 1,186 counties;
• 542 Micropolitan Statistical Areas, which contain 658 counties;
• 37 Metropolitan Divisions;
• 184 Combined Statistical Areas; and
• 1,300 counties outside of the CBSA classification.

Through Bulletin No. 23-01, OMB reinforces that the delineations for CBSAs are "solely for statistical purposes."

Issues for Congress

Though CBSAs are delineated solely for statistical purposes, their practical use in federal programs has attracted congressional interest. Areas of interest for Congress may include

• what federal agencies or programs use CBSAs for nonstatistical purposes;
• how delineating CBSAs solely for statistical purposes impacts their nonstatistical uses;
• how changes to CBSA delineations may impact delivery of services and benefits in federal programs;
• instances in which laws use CBSA delineations as the basis for defining other geographic areas; and
• general oversight of implementation of CBSA revisions.