An area's geographic context has a significant effect on its
development. Economic opportunities accrue to a place by virtue
of both its size and its access to larger economies. And, access
to larger economies—centers of information, communication,
trade, and finance—enables a smaller economy to connect to
national and international marketplaces. These relationships among
economies are basic concepts of the central place theory commonly
studied in regional economics. Population size, urbanization, and
access to larger communities are often crucial elements in research
dependent on county-level data sets. To further such research,
ERS developed a set of county-level urban influence categories
that captures some differences in economic opportunities.
The 2003 Urban Influence Codes divide the 3,141 counties, county
equivalents, and independent cities in the United States into 12
groups. Metro counties are divided into two groups by the size of the metro
area—those
in "large" areas with at least 1 million residents and
those in "small" areas with fewer than 1 million residents.
Nonmetro micropolitan counties
are divided into three groups by their adjacency to metro areas—adjacent
to a large metro area, adjacent to a small metro area, and not
adjacent to a metro area.
Nonmetro noncore counties
are divided into seven groups by their adjacency to metro or micro
areas and whether or not they have their "own
town" of at least 2,500 residents. Census-defined places are
considered to be towns in this classification. Independent cities
of Virginia have been combined with their counties of origin, and
Kalawao County Hawaii has been combined with Maui County.
2003 Urban Influence Codes |
Code |
Description |
Number of counties |
2000 Population |
Square miles |
Population
per sq. mile |
Metropolitan counties: |
1
|
In large metro area of 1+ million residents |
413 |
149,224,067 |
267,423 |
558.0 |
2
|
In small metro area of less than 1 million residents |
676 |
83,355,873 |
629,671 |
132.4 |
Nonmetropolitan counties: |
3 |
Micropolitan area adjacent to large metro area |
92 |
5,147,233 |
94,178 |
54.7 |
4 |
Noncore adjacent to large metro area |
123 |
2,364,159 |
88,229 |
26.8 |
5 |
Micropolitan area adjacent to small metro area |
301 |
14,668,144 |
285,527 |
51.4 |
6 |
Noncore adjacent to small metro area and contains a town
of at least 2,500 residents |
358 |
7,855,590 |
334,361 |
23.5 |
7 |
Noncore adjacent to small metro area and does not contain a town
of at least 2,500 residents |
185 |
1,879,264 |
336,499 |
5.6 |
8 |
Micropolitan area not adjacent to a metro area |
282 |
9,139,821 |
338,256 |
27.0 |
9 |
Noncore adjacent to micro area and contains a town of at least 2,500 residents |
201 |
3,227,833 |
193,200 |
16.7 |
10 |
Noncore adjacent to micro area and does not contain a town of
at least 2,500 residents |
198 |
1,313,175 |
196,269 |
6.7 |
11 |
Noncore not adjacent to metro or micro area and contains a town of at least 2,500 residents |
138 |
2,247,189 |
488,521 |
4.6 |
12 |
Noncore not adjacent to metro or micro area and does not contain a town of at least 2,500 residents |
174 |
999,558 |
285,304 |
3.5 |
Total U.S. |
3,141 |
281,421,906 |
3,537,438 |
79.6 |
Description of the 1993
Urban Influence Codes.
Urban influence codes group metro and nonmetro counties according
to the official metro status announced by the Office
of Management and Budget (OMB) (See new
definitions in 2003 for more information) in
June 2003, based on population and commuting data from the 2000
Census of Population. Nonmetro counties are defined as adjacent if they abut a metro area (noncore also if
they abut a micro area) and have at least 2 percent of employed
persons commuting to work in the core of the metro area (or in
the micro area). When a nonmetro county met the adjacency criteria
to more than one metro (or micro) area, it was designated as adjacent
to the area to which the largest percentage of its workers commuted.
In concept, the 2003 version of the Urban Influence Codes is comparable
with those of earlier decades. However, OMB made major changes
in its metro area delineation procedures for the 2000 Census, and
the Census Bureau changed the way in which rural and urban are
measured. Therefore, the new Urban Influence Codes are not fully
comparable with those of earlier years. OMB's changes added some
additional metro areas by no longer requiring that a metro area
must have at least 100,000 population if its urbanized area has
no place of at least 50,000 people. More importantly, simplifying
the worker commuting criteria that determine outlying metro counties
had the effect of both adding numerous new outlying counties to
metro status while deleting a smaller number that were previously
metro.
The Census Bureau made a radical shift in determining rural-urban
boundaries by changing and liberalizing the procedures for delineating
urbanized areas of 50,000 or more people, and abandoning place
boundaries in measuring urban or rural population (See what
is rural? for more information). The procedures used in defining Urbanized
Areas were extended down to clusters
of 2,500 or more people, based solely on population density per
square mile. In this manner, lightly settled sections of municipalities
were treated as rural, and densely settled areas adjoining urban
cores were treated as urban, regardless of whether they were incorporated
or not. Thus "urban clusters" need not necessarily have
at least one incorporated or unincorporated place of 2,500 population,
and not all incorporated or unincorporated places of 2,500 population
constitute urban clusters. On balance, these completely computerized
techniques for identifying and bounding urban areas have enlarged
the urban population. It is not possible to redefine Urban Influence
Codes for prior censuses in a manner consistent with those of
2003.
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