The United States Office of Management and Budget (OMB) has defined 381 Metropolitan Statistical Areas (MSAs) for the United States and seven for Puerto Rico. The OMB defines a Metropolitan Statistical Area as one or more adjacent counties or county equivalents that have at least one urban core area of at least 50,000 population, plus adjacent territory that has a high degree of social and economic integration with the core as measured by commuting ties.
An enlargeable map of the 929 Core Based Statistical Areas (CBSAs) of the United States and Puerto Rico. The 388 Metropolitan Statistical Areas (MSAs) are shown in medium green. The 541 Micropolitan Statistical Areas (μSAs) are shown in light green.
^ a b c d e "OMB Bulletin No. 13-01: Revised Delineations of Metropolitan Statistical Areas, Micropolitan Statistical Areas, and Combined Statistical Areas, and Guidance on Uses of the Delineations of These Areas" (PDF).
^ a b The United States Office of Management and Budget (OMB) defines a Combined Statistical Area (CSA) as an aggregate of adjacent Core Based Statistical Areas that are linked by commuting ties.