The term Metropolitan has many definitions, and for the purposes of the Center we use the 2013 U.S. Office of Management and Budget’s county-based definition (.pdf).
U.S. Office of Management and Budget Definition
The U.S. Office of Management and Budget (OMB) classifies counties as metropolitan if they contain an urbanized area of 50,000 or more population, or are adjacent to such a county and linked to it based on a high degree of social and economic integration with the core as measured by commuting ties. All other counties are designated nonmetropolitan by the OMB.
Rural-Urban Continuum Codes (RUCC) adds nuance to the Metropolitan designation assigned to counties by the OMB. The RUCC is a classification scheme developed by the U.S. Department of Agriculture (USDA) Economic Research Service (ERS) that distinguishes metropolitan counties by the population size of their metro area, and nonmetropolitan counties by their degree of urbanization and adjacency to a metro area. It subdivides the official OMB metro and nonmetropolitan categories into three metro and six nonmetropolitan categories. Each county in the U.S. is assigned one of the 9 codes.
Under the RUCC scheme, the following codes differentiate metropolitan counties
1: Counties in metro areas of 1 million population or more
2: Counties in metro areas of 250,000 to 1 million population
3: Counties in metro areas of fewer than 250,000 population
A cross-walk for these two approaches to defining metropolitan (.pdf) provides the:
- Metropolitan Statistical Area (MSA)
- principle cities that make up the MSA
- counties that make up the MSA, and
- Rural-Urban Continuum Code associated with the MSA