The United States federal government defines and delineates the nation's metropolitan areas for statistical purposes, using a set of standard statistical area definitions. As of 2020, the U.S. Office of Management and Budget (OMB) defined and delineated 392 metropolitan statistical areas (MSAs) and 547 micropolitan statistical areas (μSAs) in the United States and Puerto Rico. Many of these 939 MSAs and μSAs are, in turn, components of larger combined statistical areas (CSAs) consisting of adjacent MSAs and μSAs that are linked by commuting ties; as of 2020, 551 metropolitan and micropolitan areas are components of the 175 defined CSAs. A collective term for MSAs, μSAs, and CSAs is primary statistical areas (PSAs), though that term is not used by OMB.
Metropolitan and micropolitan statistical areas are defined as consisting of one or more adjacent counties or county equivalents with at least one urban core area meeting relevant population thresholds, plus adjacent territory that has a high degree of social and economic integration with the core, as measured by commuting ties. A metropolitan statistical area has at least one urban core with a population of at least 50,000. In a micropolitan statistical area, the largest urban core has a population of at least 10,000 but less than 50,000.

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