1990 Rural-urban commuting area codes

A flexible approach to delineating components of the U.S. settlement system has been developed using census tracts instead of counties. Like the widely used metropolitan areas, the rural-urban commuting area code is based on measures of urbanization, population density, and daily commuting. Metro areas are defined by Office of Management and Budget for purposes of collecting, tabulating, and publishing Federal data. They have been used from early on for analyzing societal needs and for developing programs to address those needs. However, they are not adequate for many current applications, for two reasons. First, the system is limited to identifying cities of 50,000 or more and their outlying suburbs, leaving the remaining nonmetro component undifferentiated. Second, metro areas are identified using counties as the basic building blocks. The inconsistent size of counties sometimes creates a mismatch between the defined areas and actual research or programmatic needs.

The particular system presented here is specifically designed to address these shortcomings and to highlight nonmetro settlement diversity. Census tracts are used because they are the smallest geographic building block for which reliable commuting data are available. The classification contains 10 primary and 30 secondary codes. Few if any applications need the full set of codes. Rather, the system allows for the selective combination of codes to meet varying definitional needs.

The 10 whole numbers shown in Table 1 below refer to the primary or single largest commuting share (an additional code, 99, is used for tracts with little or no population and no commuting flows). Metro area cores (code 1) are not defined by incorporated place boundaries but instead are a census tract equivalent to the census-defined urbanized area. Tracts are included if more than 20 percent of the tract's population is in the urbanized area. For nonmetro cities and towns, the cores similarly include census tracts with more than 20 percent of the population in places that make up the agglomeration—either an incorporated town or an unincorporated (census designated) place.

High commuting (codes 2, 5, and 8) means that the largest commuting share was at least 30 percent to an urbanized area, large town, or small town core. Large or small town cores (and even a few urbanized areas) can have high enough out-commuting to be coded 2, 5, or 8; typically these areas are not job centers themselves but depend on this commuting to a nearby, larger place. Low commuting (codes 3, 6, and 9) refers to cases where the single largest flow is to a core, but is less than 30 percent. These codes identify "influence areas" of metro, large town, and small town cores, respectively, and are similar in concept to the "nonmetropolitan adjacent" codes found in other ERS classification schemes (Rural-Urban Continuum Code, Urban Influence Code). The last of the general classification codes (10) identifies rural tracts where the primary flow is local.

These 10 codes offer a relatively straightforward and complete delineation of metropolitan and nonmetropolitan settlement based on the size and direction of primary commuting flows. However, the settlement world is not that simple. One confounding factor is "hierarchical relations" or semiautonomous relations of a place to another place. The 10 broad classification codes are subdivided to identify areas where the primary flow is local, but over 30 percent commute in a secondary flow to a larger area core. For example, 1.1 and 2.1 codes identify urbanized areas and their outlying commuter zones where the primary flow is within or to the urbanized area, but another 30 percent or more commute to a larger urbanized area. Similarly, 10.1, 10.2, and 10.3 identify rural tracts for which the primary commuting share is local but more than 30 percent also commute to a metro, large town, or small town core, respectively.

Influence areas for metropolitan and large town cores extend far beyond the relatively small number identified on the basis of primary flows (codes 3 and 6). Codes 7 to 10 were subdivided to identify small town and rural tracts with primary local flows but secondary flows of 5 to 30 percent, either to a metropolitan or large town core. These areas identify important, potentially metropolitanizing zones within current nonmetropolitan territory.

Finally, examination of States with fairly closely spaced metropolitan areas reveals examples of tracts for which no single urbanized area commuting share exceeds 30 percent, but for which shares to multiple metropolitan areas may be quite high. We code these areas as 2.2. Similarly, a small number of tracts coded 4.1, 7.1, 7.2, 10.1, or 10.2 (secondary flow 30% to 50% to a UA or large town) are based on shares to multiple cores.

The codes are many, but permit stricter or looser delimitation of metropolitan, large town, and small town commuting areas. This scheme replaces the county-based, default nonmetropolitan category with a subcounty settlement system, including areas of metropolitan influence and an urban-rural hierarchy, thus providing an exhaustive system of statistical areas for the country.

Table 1. Rural-Urban Commuting Areas (RUCAs)
1  Metropolitan-area core: primary flow within an urbanized area (UA)
1.0	No additional code
1.1	Secondary flow 30% to 50% to a larger UA
2  Metropolitan-area high commuting: primary flow 30% or more to a UA
2.0	Primary flow to a 1.0 UA
2.1	Primary flow to a 1.1 UA
2.2	Combined flows to two or more UAs adding to 30% or more
3  Metropolitan-area low commuting: primary flow 5% to 30% to a UA
3.0	No additional code
4  Large town core: primary flow within a place of 10,000 to 49,999
4.0	No additional code
4.1	Secondary flow 30% to 50% to a UA
5  Large town high commuting: primary flow 30% or more to a place of 10,000 to 49,999
5.0	Primary flow to a 4.0 large town
5.1	Primary flow to a 4.1 large town
6  Large town low commuting: primary flow 5% to 30% to a place of 10,000 to 49,999
6.0	No additional code
7  Small town core: primary flow within a place of 2,500 to 9,999 7.0 No additional code
7.0	No additional code
7.1	Secondary flow 30% to 50% to a UA
7.2	Secondary flow 30% to 50% to a large town
7.3	Secondary flow 5% to 30% to a UA
7.4	Secondary flow 5% to 30% to a large town
8  Small town high commuting: primary flow 30% or more to a place of 2,500 to 9,999
8.0	Primary flow to a 7.0 small town
8.1	Primary flow to a 7.1 small town
8.2	Primary flow to a 7.2 small town
8.3	Primary flow to a 7.3 small town
8.4	Primary flow to a 7.4 small town
9  Small town low commuting: primary flow 5% to 30% to a place of 2,500 to 9,999
9.0	No additional code
9.1	Secondary flow 5% to 30% to a UA
9.2	Secondary flow 5% to 30% to a large town
10  Rural areas: primary flow to a tract without a place of 2,500 or more
10.0	No additional code
10.1	Secondary flow 30% to 50% to a UA
10.2	Secondary flow 30% to 50% to a large town
10.3	Secondary flow 30% to 50% to a small town
10.4	Secondary flow 5% to 30% to a UA
10.5	Secondary flow 5% to 30% to a large town
99  Not coded: Tracts with little or no population and no commuting flows

A ZIP code approximation of the RUCA codes is also available. It is based on a ZIP/Census tract crosswalk and not on a separate analysis of population and commuting data unique to the ZIP code geographic unit.

This research was sponsored and funded by ERS and the Health Resources and Services Administration's Federal Office of Rural Health Policy (ORHP), and executed at the WWAMI Rural Research Center at the University of Washington. For further information, see Morrill, Richard, John Cromartie, and Gary Hart. 1999. "Metropolitan, Urban, and Rural Commuting Areas: Toward a Better Depiction of the United States Settlement System." Urban Geography 20: 727-748.

Download the 1990 Rural-Urban Commuting Area Codes

Learn more about the ZIP code approximation of the RUCA codes at University of Washington.

for more information, contact: John Cromartie
web administration: webadmin@ers.usda.gov
page updated: January 20, 2004