Documentation
2000 Rural-Urban Commuting Area Codes
The Rural-Urban commuting area (RUCA) codes, a detailed and
flexible scheme for delineating sub-county components of the U.S.
settlement system, have been updated using data from the 2000
decennial census. RUCA codes are based on the same theoretical
concepts used by the Office of Management and Budget (OMB) to
define county-level metropolitan and micropolitan areas. We applied similar
criteria to measures of population density, urbanization, and daily
commuting to identify urban cores and adjacent territory that is
economically integrated with those cores. We adopted OMB's
metropolitan and micropolitan terminology to highlight the
underlying connectedness between the two classification systems.
However, the use of census tracts instead of counties as building
blocks for RUCA codes provides a different and more detailed
geographic pattern of settlement classification.
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, research or policy 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.
Metropolitan cores (code 1) are defined as census tract equivalents
of urbanized areas. Micropolitan and small town
cores (codes 4 and 7, respectively) are tract equivalents of urban clusters. Tracts are included in urban
cores if more than 30 percent of their population is in the
urbanized area or urban cluster.
High commuting (codes 2, 5, and 8) means that the largest
commuting share was at least 30 percent to a metropolitan,
micropolitan, or small town core. Many micropolitan and small town
cores themselves (and even a few metropolitan cores) have high
enough out-commuting to other cores to be coded 2, 5, or 8;
typically these areas are not job centers themselves but serve as
bedroom communities for a nearby, larger city. 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, micropolitan, 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 or to
another rural tract.
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. The primary RUCA codes are
further subdivided to identify areas where settlement
classifications overlap, based on the size and direction of the
secondary, or second largest, commuting flow. For example, 1.1 and
2.1 codes identify areas where the primary flow is within or to a
metropolitan core, but another 30 percent or more commute to a
larger metropolitan core. 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 metropolitan, micropolitan,
or small town core, respectively.
Influence areas for urban cores extend far beyond the relatively
small number identified on the basis of primary flows (codes 3, 6,
and 9). Codes 4-10 were subdivided to identify micropolitan, small
town, and rural tracts with secondary flows of 10 to 30 percent to
larger urban cores. This strategy identifies important, potentially
urbanizing zones within current nonmetropolitan territory.
RUCA codes are many, but permit stricter or looser delimitation
of metropolitan, micropolitan, and small town commuting areas. This
classification scheme provides an alternative to county-based
systems for situations where more detailed geographic analysis is
feasible. It identifies areas of emerging urban influence and areas
where settlement classifications overlap, thus providing an
exhaustive system of statistical areas for the country.
| Table 1.
Rural-Urban Commuting Areas (RUCAs), 2000 |
| 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 |
No additional code |
| 2.1 |
Secondary flow 30% to 50% to a larger UA |
| 3 Metropolitan area low commuting: primary
flow 5% to 30% to a UA |
| 3.0 |
No additional code |
| 4 Micropolitan area core: primary flow within an
Urban Cluster of 10,000 to 49,999 (large UC) |
| 4.0 |
No additional code |
| 4.1 |
Secondary flow 30% to 50% to a UA |
| 4.2 |
Secondary flow 10% to 30% to a UA |
| 5 Micropolitan high commuting: primary flow 30% or
more to a large UC |
| 5.0 |
No additional code |
| 5.1 |
Secondary flow 30% to 50% to a UA |
| 5.2 |
Secondary flow 10% to 30% to a UA |
| 6 Micropolitan low commuting: primary flow 10% to
30% to a large UC |
| 6.0 |
No additional code |
| 6.1 |
Secondary flow 10% to 30% to a UA |
| 7 Small town core: primary flow within an Urban
Cluster of 2,500 to 9,999 (small UC) |
| 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 UC |
| 7.3 |
Secondary flow 10% to 30% to a UA |
| 7.4 |
Secondary flow 10% to 30% to a large UC |
| 8 Small town high commuting: primary flow 30% or
more to a small UC |
| 8.0 |
No additional code |
| 8.1 |
Secondary flow 30% to 50% to a UA |
| 8.2 |
Secondary flow 30% to 50% to a large UC |
| 8.3 |
Secondary flow 10% to 30% to a UA |
| 8.4 |
Secondary flow 10% to 30% to a large UC |
| 9 Small town low commuting: primary flow 10% to 30%
to a small UC |
| 9.0 |
No additional code |
| 9.1 |
Secondary flow 10% to 30% to a UA |
| 9.2 |
Secondary flow 10% to 30% to a large UC |
| 10 Rural areas: primary flow to a tract
outside a UA or UC |
| 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 UC |
| 10.3 |
Secondary flow 30% to 50% to a small UC |
| 10.4 |
Secondary flow 10% to 30% to a UA |
| 10.5 |
Secondary flow 10% to 30% to a large UC |
| 10.6 |
Secondary flow 10% to 30% to a small UC |
A ZIP code approximation of the RUCA codes is also available. It
is based on an overlay of ZIP code areas on census tracts 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
Geography20: 727-748.
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 2
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.
On February 1, 2001, secondary RUCA codes for 511 tracts were
changed because the tracts did not meet the required commuting
threshold. The 511 tracts had secondary commuting flows between 25
to 30 percent but had been given codes requiring 30 percent or
more. Primary (whole number) codes were not affected.
| Table 2.
Rural-Urban Commuting Areas (RUCAs), 1990 |
| 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
Geography20: 727-748.
Learn more about the ZIP code approximation of the
RUCA codes at University of Washington.