Source: U.S. Bureau of the Census: Metropolitan Areas. New areas
usually are added annually; definitions of existing areas
updated only after each decennial census, in years ending in 3.
http://www.census.gov/population/metro/ The general concept of a
metropolitan area is that of a large population nucleus,
together with adjacent communities having a high degree of
social and economic integration with that core. Metropolitan
areas comprise one or more entire counties, except in New
England, where cities and towns are the basic geographic units.
The Office of Management and Budget (OMB) defines metropolitan
areas for purposes of collecting, tabulating, and publishing
federal data. Metropolitan area definitions result from applying
published standards to Census Bureau data. A metropolitan areas
identified as a consolidated metropolitan statistical area
(CMSA) has a population of one million or more and also has
separate component areas (PMSAs - primary metropolitan
statistical areas) meeting statistical criteri