Researchers and policy officials employ many definitions to distinguish rural from urban areas, which often leads to unnecessary confusion and unwanted mismatches in program eligibility. However, the existence of multiple rural definitions reflects the reality that rural and urban are multidimensional concepts. Sometimes population density is the defining concern, in other cases it is geographic isolation. Small population size typically characterizes a rural place, but how small is rural? Population thresholds used to differentiate rural and urban communities range from 2,500 up to 50,000, depending on the definition.
Because the U.S. is a nation in which so many people live in areas that are not clearly rural or urban, seemingly small changes in the way rural areas are defined can have large impacts on who and what are considered rural. Researchers and policymakers share the task of choosing appropriately from among alternate rural definitions currently available or creating their own unique definitions.
Nonmetro Counties are Commonly Used to Depict Rural and Small-Town Trends
ERS researchers and others who analyze conditions in "rural" America most often use data on nonmetropolitan (nonmetro) areas, defined by the Office of Management and Budget (OMB) on the basis of counties or county-equivalent units (e.g., parishes, boroughs). Counties are the standard building block for publishing economic data and for conducting research to track and explain regional population and economic trends. Estimates of population, employment, and income are available for them annually. They also are frequently used as basic building blocks for areas of economic and social integration, such as labor-market areas.
A regional-economic concept underlies the formation of the metropolitan-nonmetropolitan classification. (For a detailed comparison of economic, land-use, and administrative concepts underlying different rural definitions, see Defining the "Rural" in Rural America, Amber Waves, June 2008.) In 2013, OMB defined metropolitan (metro) areas as broad labor-market areas that include:
- Central counties with one or more urbanized areas; urbanized areas (described in the next section) are densely-settled urban entities with 50,000 or more people.
- Outlying counties that are economically tied to the core counties as measured by labor-force commuting. Outlying counties are included if 25 percent of workers living in the county commute to the central counties, or if 25 percent of the employment in the county consists of workers coming out from the central counties—the so-called "reverse" commuting pattern.
Nonmetro counties are outside the boundaries of metro areas and are further subdivided into two types:
- Micropolitan (micro) areas, which are nonmetro labor-market areas centered on urban clusters of 10,000-49,999 persons and defined with the same criteria used to define metro areas.
- All remaining counties, often labeled “noncore” counties because they are not part of “core-based” metro or micro areas;
Every 10 years, following the decennial census, nonmetro counties that have been growing rapidly enough or experiencing increasing commuting are reclassified as metro. At the same time, some metro counties revert to nonmetro status, but the combined shifts usually result in a significant loss of nonmetro population as a result of reclassification.
Census Bureau Defines Urban and Rural Areas on the Basis of Population Density
A very different definition of rural, based on much smaller geographic building blocks, is provided by the U.S. Census in its urban-rural classification system. Whereas researchers often use the term rural when referring to nonmetro areas, and Congressional legislation uses the term when describing different targeting definitions, the Census Bureau provides the official, statistical definition of rural, based strictly on measures of population size and density. According to the current delineation, released in 2012 and based on the 2010 decennial census, rural areas comprise open country and settlements with fewer than 2,500 residents. Urban areas comprise larger places and densely settled areas around them. Urban areas do not necessarily follow municipal boundaries. They are essentially densely settled territory as it might appear from the air. Most counties, whether metro or nonmetro, contain a combination of urban and rural populations.
Urban areas are of two types--urbanized areas and urban clusters--identical in the criteria used to delineate them but different in size. The Census Bureau defines an urbanized area wherever it finds an urban nucleus of 50,000 or more people. They may or may not contain any individual cities of 50,000 or more. In general, they must have a core with a population density of 1,000 persons per square mile and may contain adjoining territory with at least 500 persons per square mile. Urbanized areas have been delineated using the same basic threshold (50,000 population) for each decennial census since 1950, but procedures for delineating the urban fringe are more liberal today.
The same computerized procedures and population density criteria are used to identify urban clusters of at least 2,500 but less than 50,000 persons. This delineation of built-up territory around small towns and cities was first introduced in 2000. According to this system, rural areas consist of open countryside with population densities less than 500 people per square mile and places with fewer than 2,500 people.
OMB "Nonmetro" and Census "Rural" Provide Different but Equally Useful Perspectives on Rural Populations
The choice of a rural definition should be based on the purpose of the application, whether that application is for research, policy analysis, or program implementation. For instance, tracking urbanization and its influence on farmland prices is best approached using the Census urban-rural definition because it is a land-use definition that distinguishes built-up territory from immediately surrounding, less developed land. Studies designed to track and explain economic and social changes often choose to use the metro-nonmetro classification, because it reflects a regional, labor-market concept and allows the use of widely available county-level data. The key is to use a rural-urban definition that best fits the needs of a specific activity, recognizing that any simple dichotomy hides a complex rural-urban continuum, often with very gentle gradations from one level to the next.
Office of Management and Budget, Standards for Delineating Metropolitan and Micropolitan Statistical Areas: http://www.whitehouse.gov/sites/default/files/omb/assets/fedreg_2010/06282010_metro_standards-Complete.pdf
Office of Management and Budget (OMB), Metropolitan and Micropolitan Delineation Files, February 2013: http://www.census.gov/population/metro/data/def.html
U.S. Census Bureau, Metropolitan and Micropolitan Statistical Areas: http://www.census.gov/population/metro/
U. S. Census Bureau, Urban Area Criteria for the 2010 Census: http://www.census.gov/geo/reference/pdfs/fedreg/fedregv76n164.pdf
U.S. Census Bureau, Urban and Rural Classification: http://www.census.gov/geo/reference/urban-rural.html