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.