As defined and designated by the U. S. Office of Management and Budget, an MSA consists of the central county or counties containing a city or an urbanized area with a population of at least 50,000 and the adjacent or outlying counties that have close economic and social relationships with the central counties, with a total metropolitan population of at least 100,000. An MSA, in contrast to the urbanized area, will therefore correspond to existing political jurisdiction boundaries (i.e., entire counties, except in the six New England states, where the boundaries are in terms of cities and towns. The term was adopted after the 1980 census and replaces standard metropolitan statistical area (SMSA). (TRB)