Metropolitan Area Designations by OMB: History, Current Definitions, and Uses [November 15, 2004] [open pdf - 44KB]
From the Summary: "On December 27, 2000, the Office of Management and Budget (OMB) announced its uniform criteria, or 'standards,' for defining metropolitan and micropolitan statistical areas in the current decade. These areas together are termed 'core based statistical areas' (CBSAs). Also announced were the standards for defining New England city and town areas (NECTAs), which are conceptually similar to CBSAs. The 2000 standards superseded those for defining metropolitan statistical areas in the 1990s. CBSAs consist of counties and county-equivalents in the United States and Puerto Rico. Each CBSA must contain at least one urbanized area of 50,000 or more persons (metropolitan statistical area) or at least one urban cluster of 10,000 to 49,999 persons (micropolitan statistical area). CBSAs have one or more principal cities and central counties. Outlying counties are included in CBSAs on the basis of commuting data. Counties that do not meet the criteria for inclusion in CBSAs are classified as 'outside core based statistical areas.' NECTAs are classified similarly to CBSAs and designated as either 'metropolitan' or 'micropolitan' NECTAs."
CRS Report for Congress, RL32675