The general concept of a metropolitan or micropolitan statistical area is that of a core area containing a substantial population nucleus, together with adjacent communities having a high degree of economic and social integration with that core. Currently defined metropolitan and micropolitan statistical areas are based on application of 2000 standards (which appeared in the Federal Register on December 27, 2000) to 2000 decennial census data. Current metropolitan and micropolitan statistical area definitions were announced by OMB effective June 6, 2003.

The term "core based statistical area" (CBSA) became effective in 2000 and refers collectively to metropolitan and micropolitan statistical areas.