A metropolitan or micropolitan statistical area's geographic composition, or list of geographic components at a particular point in time, is referred to as its "delineation." Metropolitan and micropolitan statistical areas are delineated by the U.S. Office of Management and Budget (OMB) and are the result of the application of published standards to Census Bureau data. The standards for delineating the areas are reviewed and revised once every ten years, prior to each decennial census. Generally, the areas are delineated using the most recent set of standards following each decennial census. Between censuses, the delineations are revised to reflect Census Bureau population estimates and--once each decade--updated commuting-to-work data. Areas based on the 2010 standards and Census Bureau data were delineated in February of 2013, and updated in July of 2015, August of 2017, April of 2018, September of 2018, and March of 2020.
The files below show delineations of metropolitan and micropolitan statistical areas and related statistical areas delineated by OMB since February 2013, including the most recent March 2020 delineations. Related statistical areas include New England city and town areas (NECTAs), which are conceptually similar to metropolitan and micropolitan statistical areas, but are delineated using cities and towns instead of counties; combined statistical areas, which are aggregates of adjacent metropolitan or micropolitan statistical areas that are linked by commuting ties; combined New England city and town areas, which are aggregates of adjacent NECTAs that are linked by commuting ties; metropolitan divisions, which are a county or group of counties (or equivalent entities) delineated within a larger metropolitan statistical area, provided that the larger metropolitan statistical area contains a single core with a population of at least 2.5 million and other criteria are met; and NECTA divisions, which are a city or town, or group of cities and towns, delineated within a NECTA, provided that the NECTA contains a single core with a population of at least 2.5 million and other criteria are met.