Table 1.

US^† rural-urban classification systems

Source	Description of rural and urban areas
2010 US Census Bureau14,84	Urban: territory, population, and housing units located within UAs‡ (population ≥50,000) and UCs§ (2,500≤ population <50,000) Rural: all non-urban areas
USDA Economic Research Service15	Frontier and Remote Area (FAR) codes ‘Frontier and remote’ describes territory characterized by combination of low population size and high geographic remoteness. Based on 2010 US census, four codes are defined in relation to the time it takes to travel by car to the edges of nearby UAs. i. Level one FAR approximates remoteness from UAs of ≥50,000 people ii. Level two FAR approximates remoteness from UAs of ≥25,000 people iii. Level three FAR approximates remoteness from UAs of ≥10,000 people iv. Level four FAR shows remoteness from UA of ≥2,500 people
Office of Management and Budget (OMB)16	County-level designation based on population density and commuting: Metropolitan statistical areas: i. contain a core urban area with one or more UAs (population ≥50,000), and ii. adjacent counties with high degree of social and economic integration to the core UAs, measured by labor-force commuting Nonmetropolitan areas outside of the boundaries of metropolitan areas and subdivided in to: i. micropolitan statistical areas centered on UCs (10,000≤ population <50,000) ii. noncore areas not included in metropolitan and micropolitan areas Metropolitan areas are generally considered urban, and nonmetropolitan areas are generally considered rural.
National Center for Health Statistics (Centers for Disease Control and Prevention)17	County-level designation Metropolitan counties i. Large central metropolitan: counties in metropolitan statistical areas (MSA) of ≥1 million population that: • contain the entire population of the largest principal city of the MSA, or • are completely contained within the largest principal city of the MSA, or • contain at least 250,000 residents of any principal city in the MSA ii. Large fringe metropolitan: counties in MSAs of ≥1 million population that do not qualify as large central metro counties iii. Medium metropolitan: counties in MSAs of 250,000–999,999 population iv. Small metropolitan: counties in MSAs of <250,000 population Nonmetropolitan counties i. Micropolitan: counties in micropolitan statistical areas ii. Noncore: nonmetropolitan counties that do not qualify as micropolitan
United States Department of Agriculture (USDA) Economic Research Service18	Rural-urban continuum codes (RUCC) based on OMB codes, and developed in 2013. Metropolitan counties: i. counties in metropolitan areas with population ≥1 million ii. counties in metropolitan areas with population 250,000 – 1 million iii. counties in metropolitan areas with population <250,000 Nonmetropolitan counties: i. urban population ≥20,000, adjacent to a metropolitan area ii. urban population ≥20,000, not adjacent to a metropolitan area iii. urban population 2,500 – 19,999, adjacent to a metropolitan area iv. urban population 2,500 – 19,999, not adjacent to a metropolitan area v. completely rural or <2,500 urban population, adjacent to a metropolitan area vi. completely rural or <2,500 urban population, not adjacent to a metropolitan area Unknown-Alaska/Hawaii State/not official USDA Rural-Urban Continuum code Unknown/not official USDA Rural-Urban Continuum code
Health Resources and Services Administration’s (HRSA’s) Office of Rural Health Policy; USDA’s Economic Research Service; WWAMI Rural Health Research Center19	Rural-Urban Commuting Area (RUCA) codes are an alternative to the county-level classification system. RUCA codes classify US census tracts using measures of population density, urbanization, and daily commuting. Metropolitan area core: primary flow within a UA Metropolitan area high commuting: primary flow 30% or more to a UA Metropolitan area low commuting: primary flow 10% to 30% to a UA Micropolitan area core: primary flow within a UC of 10,000 to 50,000 (large UC) Micropolitan high commuting: primary flow 30% or more to a large UC Micropolitan low commuting: primary flow 10% to 30% to a large UC Small town core: primary flow within a UC of 2,500 to 9,000 (small UC) Small town core: primary flow 30% or more to a small UC Small town low commuting: primary flow 10% to 30% to a small UC Rural areas: primary flow to a tract outside a UA or UC Sub-codes present within each category, as described.19
USDA Economic Research Service20	Urban Influence Codes Metropolitan counties i. In large metropolitan area of ≥1 million population ii. In small metropolitan area of <1 million population Nonmetropolitan counties i. Micropolitan area adjacent to large metropolitan area ii. Noncore adjacent to large metropolitan area iii. Micropolitan area adjacent to small metropolitan area iv. Noncore adjacent to small metropolitan area and contains a town of ≥2,500 population v. Noncore adjacent to small metropolitan area and contains a town of <2,500 population vi. Micropolitan area not adjacent to a metro area vii. Noncore adjacent to micro area and contains a town of at least 2,500 residents viii. Noncore adjacent to micro area and does not contain a town of at least 2,500 residents ix. Noncore not adjacent to metro or micro area and contains a town of at least 2,500 residents x. Noncore not adjacent to metro or micro area and does not contain a town of at least 2,500 residents

^†US: United States;

^‡UA: urbanized area;

^§UC: urban cluster