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The Bureau of the Census defines urban as comprising all territory, popu- lation, and housing units located in urbanized areas and in places of 2, or more inhabitants outside of UAs. The term urban refers to both kinds of geographic entities. The terms urban , urbanized area , and rural are the Census Bureau’s definitions; other Federal agencies, State agencies, local officials, and private groups may use these same terms to identify areas based on different criteria.
Urbanized Areas (UAs) A UA is a continuously built-up area with a population of 50,000 or more. It comprises one or more places— central place(s) —and the adjacent densely settled surrounding area— urban fringe —consisting of other places and nonplace territory.
Urban Places Outside of UAs Outside of UAs, an urban place is any incorporated place or census des- ignated place (CDP) with at least 2,500 inhabitants. A CDP is a densely settled population center that has a name and community identity, and is not part of any incorporated place (see Chapter 9, “Places”).
Rural Places and Territory Territory, population, and housing units that the Census Bureau does not classify as urban are classified as rural. For instance, a rural place is any incorporated place or CDP with fewer than 2,500 inhabitants that is located outside of a UA. A place is either entirely urban or entirely rural, except for those designated as an extended city.
Extended Cities An extended city is an incorporated place that contains large expanses of sparsely populated territory for which the Census Bureau provides sepa- rate urban and rural population counts and land area figures.
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The Urban and Rural Classifications
Chapter 12
Components of the Urban and Rural Classifications
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The Census Bureau defines UAs and extended cities for statistical purposes only; that is, for the purpose of presenting its data. Although some other geographic statistical entities, such as census tracts and CDPs, originate from agreement and cooperative action with local governmental officials and other outside groups, the development and implementation of cri- teria for defining and delineating UAs and extended cities has been largely the responsibility of the Census Bureau from the inception of the concept.
This chapter discusses (1) the Census Bureau’s criteria for classifying areas as urban (with an emphasis on the definition of UAs and extended cities), (2) the procedures used to establish UAs and update their boundaries, and (3) the relationship of UAs to other geographic entities. The Census Bureau applies the same urban and rural definitions to all parts of the United States, Puerto Rico, and the Outlying Areas. Puerto Rico has both UAs and urban places outside of UAs; the Outlying Areas—American Samoa, Guam, the Northern Mariana Islands, Palau, and the Virgin Islands of the United States—have only urban places.
Background
Early Definitions of Urban Statistics by urban and rural categories have figured in decennial census publications for over a century.^1 In the censuses of 1880, 1890, and 1900, the Census Office (predecessor of the Census Bureau) published tables based on minimum sizes of 8,000, 4,000, and 2,500 inhabitants; the latter figure was officially adopted for the 1910 census. In the decennial cen- suses from 1910 through 1940, urban comprised all territory, people, and housing units in incorporated places of 2,500 or more. In addition, some areas—usually minor civil divisions (MCDs) 2 —were classified as urban under special rules relating to population size and density. This definition of urban was not adequate because (1) it excluded many large, densely settled population concentrations merely because they were not part of any incorporated place, and (2) it continued to classify many large, densely built-up areas as rural in spite of the special rules that
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Table 12-1. Development of UA Criteria From 1950 Through 1990 1950 Central place requirement Incorporated place population of 50,000 or more (1940 census count) Method of boundary delineation Population estimates, precensus surveys, aerial photography Density requirement At least 500 dwelling units (approximately 2,000 people per square mile) Place population in urban fringe
- Incorporated places with at least 2,500 people; no CDPs were included
- Smaller incorporated places with a concentration of 100 or more dwelling units whose density was at least 500 dwelling units per square mile Other features Exclaves of discontiguous nonplace territory within 1 1 / 2 miles and connected by road Number of UAs A total of 157
1960 Central place requirement
- Incorporated place population of 50,000 or more using current census counts
- Twin cities rule (two contiguous incorporated places with a combined population of at least 50,000, the smaller of which must have at least 15,000) Method of boundary delineation Census results, small enumeration districts (EDs) Density requirement At least 1,000 people per square mile Place population in urban fringe At least 2,500 people; CDPs if at least 10,000 people (except New England) Other features
- MCDs in New England, New Jersey, and Pennsylvania with at least 25,000 inhabitants or a population density of at least 1,500 people per square mile and a minimum total population of 2,500 became urban by special rule ; this rule applied only to the 1960 census.
- Inclusion of indentations/enclaves
- First UAs in Hawaii and Puerto Rico Number of UAs A total of 213
1970 Central place requirement
- Incorporated place population of 50,000 or more using current census counts
- An incorporated city of 25,000 or greater population could qualify as a central place if it could combine with contiguous places of any size (but with a density of at least 1,000 people per square mile) to obtain a total population of at least 50,000. Method of boundary delineation Blocks (mail areas), small EDs (non-mail areas)
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Table 12-1. (cont.) Density requirement At least 1,000 people per square mile Place population in urban fringe
- Incorporated places with at least 2,500 people
- CDPs if at least 5,000 people (except New England)
- Some CDPs if at least 1,000 people—this lower threshold applied if an incorporated place of at least 25,000 inhabitants could join with contiguous places of any size (and a density of at least 1,000 people per square mile) to reach a total population of at least 50,000. Other features Introduction of extended cities Number of UAs A total of 275
1980 Central place requirement Incorporated place (any size) within a densely settled area of at least 50,000 population Method of boundary delineation Blocks, small EDs in certain situations Density requirement At least 1,000 people per square mile Place population in urban fringe Incorporated places of at least 2,500 people Other features
- Whole-town CDPs (MCDs in New England, Michigan, New Jersey, New York, Pennsylvania, and Wisconsin having at least 95 percent of their population and at least 80 percent of their land area qualifying for inclusion in the UA were included in their entirety in the UA—applicable only to the 1980 census).
- First CDPs in New England UAs Number of UAs A total of 366
1990 Central place requirement Incorporated place of any size within a densely settled area of at least 50,000 population; CDP of any size permitted as central place Method of boundary delineation Blocks exclusively Density requirement At least 1,000 people per square mile Place population in urban fringe Whole place test , minimum CDP population of generally 2, Other features Intercensal UAs, new titling provisions for UAs Number of UAs A total of 405
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- The whole place test improved the rules for inclusion of incorporated places and CDPs in the urban fringe. In addition, the Census Bureau introduced a standard minimum population threshold for CDPs in the urban fringe—2,500 inhabitants in most instances (see Table 12-1).
- Extended cities had been defined in 1970 and 1980 solely for UA delin- eation purposes; for 1990, the Census Bureau broadened the concept to include extended cities outside of UAs.
In addition, there were slight changes in the rules for including areas of nonresidential urban land, and more precise provisions for merging con- tiguous UAs. A major operational shift for 1990 was the introduction of an interactive delineation process and the decentralization of the UA delin- eation work, which was accomplished by the Census Bureau’s 12 regional offices, with final approval from headquarters.
Criteria for UAs and Extended Cities in the 1990 Census
A UA must exhibit a pattern of continuous development out from a central core or the boundary of a UA delineated for the previous census. Existing UAs generally retain all territory that was within their previous boundaries.^4 Areas added to the urban fringe must be contiguous to this core and must have a population density of at least 1,000 people per square mile. Areas with lower densities are permitted if they meet the criteria for jumps, non- residential urban land use, closure of indentations or enclaves, or undevel- opable territory. All area added to the UA must be connected directly by road to the main body of the UA, and this road connection must either be located within the area being added, or touch it on one side. The UA must contain at least 50,000 people.
Whole Place Qualification Places are important geographic components of UAs. Except for extended cities, all incorporated places and CDPs either are included in a UA in their entirety, or excluded from it completely. A place is included in the UA if it has a qualifying core. This qualifying core is an area with a population density of at least 1,000 people per square mile that contains at least 50 percent of
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the place’s total population and is contiguous with other qualifying urbanized territory that also meets the population density criterion. As a result of the whole place qualification rule, places with overall densities of less than 1, people per square mile may be in the UA.
Jumps A jump occurs where a low-density area is used to connect an outlying densely populated area to the main body of the UA. Two conditions must be satisfied: (1) the road distance through the low-density area must be 1 1 / 2 miles or less, and (2) the combined population density of the outlying area and the intervening area must be at least 500 people per square mile. Jumps may occur within places as well as in nonplace territory. A jump is permis- sible once along a road and in a given direction; for instance, once along Main Street to the east of the core and once along Main Street to the west of the core would both be acceptable jumps. A second jump cannot take place if it relies on a first jump for its geographic connection to the main body of the UA; for instance, a second jump east or west along Main Street.
Nonresidential Urban Land Use The UA encompasses not only densely settled residential territory, but also various nonpopulated or sparsely populated territory that serves urban func- tions and that is geographically intermingled throughout the built-up area. If population density were the sole criterion for including territory, the UA boundary could not include other adjacent densely populated territory. This would be undesirable because the low-density territory does not represent a break in settlement; rather, it includes territory with land uses that are typi- cally urban in character. Types of nonresidential urban land uses that qualify are commercial and industrial development, transportation sites, parks, golf courses, cemeteries, and the like. Their identification, in specific situa- tions, provides a more accurate UA delineation. For instance, a population density figure based only on the total surface of a small area would be lower than one that excluded its areas of nonresidential urban land use. As a result of the application of the nonresidential urban land use procedure, the popu- lation density of some territory will be greater than 1,000 people per square
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Enclaves are low-density areas surrounded by territory that is in the UA. Enclaves almost always consist of territory outside of any place (rarely are they incorporated places or CDPs); the surrounding territory may be in a place, or it may consist of nonplace territory. As with indentations, the inclusion of enclaves gives the UA a more regular appearance and simpli- fies data presentations. An enclave is included in the UA if it is five square miles or less in size and surrounded by territory that has an average den- sity of at least 1,000 people per square mile. Both conditions must apply.
Exclaves occur where an outlying piece of a place is physically separated from the main part of the place by intervening territory that does not qualify for inclusion in the UA. The intervening territory consists of either territory outside of any place or—less frequently—in another place. Places with exclaves usually are incorporated places (most CDPs consist of one contiguous piece of territory). An exclave can never consist of territory outside of any place. Exclaves always are included in the UA when their parent place is in the UA; the criteria for density, continuous develop- ment, and road connection do not apply to exclaves.
Extended Cities Some incorporated places include large expanses of vacant or very sparsely populated territory that are essentially rural in character. In general, this situation results from (1) extensive annexation of adjacent undeveloped territory, (2) governmental consolidation of an incorpo- rated place with an MCD or county, or (3) formation of a new incor- porated place from several sparsely populated MCDs.
An incorporated place is considered to be an extended city if it contains one or more areas that:
- Are 5 square miles or more in size.
- Have a population density less than 100 people per square mile.
- Comprise at least 25 percent of the total land area of the place.
- Consist of 25 square miles or more. The first two conditions, and either the third or the fourth, must apply.
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The rural portion of an extended city may consist of several separate pieces of territory, provided that each piece is at least 5 square miles in size and has a density less than 100 people per square mile. The urban portion of an extended city consists of territory that has a density of at least 100 people per square mile. Along with jumps, nonresidential urban land use, and unde- velopable territory, extended cities are another instance where portions of the UA can have a density less than 1,000 people per square mile.
The criteria for jumps, indentations, and enclaves also apply within extended cities, except that the density thresholds are lower—50 and 100 people per square mile for qualifying blocks instead of 500 and 1,000 people per square mile. If the extended city has low-density exclaves that are adjacent to its rural portions, these exclaves become part of the rural portion.
There is no minimum total population for UA extended cities; however, non- UA extended cities must have at least 2,500 inhabitants. Before the 1990 cen- sus, the Census Bureau defined extended cities only for incorporated places inside UAs. The delineation of non-UA extended cities provides better pop- ulation density statistics for the Nation’s urban population by excluding those portions of incorporated places that contain vast expanses of empty or near- empty land. (Refer to Table 9-2 in Chapter 9, “Places.”)
Qualification of UAs All candidate or potential UAs that have a 1990 census population of 50, or more qualify as UAs and appear in the 1990 census data presentations. Those potential areas that have a 1990 population below 50,000 fail to achieve urbanized status; however, their incorporated places and/or CDPs are con- sidered non-UA urban places if they have at least 2,500 inhabitants.
Retention or Merger of UAs The Census Bureau never creates a new UA from the territory of an existing UA, nor does it ever transfer large portions of populated territory from one UA to another. Where two or more UAs are contiguous, the Census Bureau decides whether to maintain separate UAs or to merge them into a single
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UA, between their core areas and the area where the two UAs meet.
- The two UAs share a common boundary line—not simply a point— that is at least 1 mile in length.
- The census blocks on both sides of this common boundary have an average density of at least 1,000 people per square mile.
The Census Bureau considers two UAs separated by less than 5 miles of water or undevelopable territory and connected by less than 5 road miles to be contiguous if the areas adjacent to the undevelopable territory and the road connection have an average population density of at least 1, people per square mile.
When two UAs touch, but do not meet all the criteria specified above, they remain separate. The separation line always follows census block boundaries, and often is a prominent physical feature or the boundary of a legal entity.
Designation of UA Central Places The central place(s) of a UA identifies the most populous center(s) or core of that UA. This designation permits data users to compare statistics for the dominant center with those for the remaining part of the UA— the urban fringe. Most UA central places are also the central cities of MAs. In rarer instances, where the UA does not contain an MA central city or the UA is located outside of an MA, the central place(s) of the UA is (are) determined by total population.
To determine central place status, the Census Bureau selects the most pop- ulous incorporated place that contains at least 2,500 people. It may select up to two additional incorporated places as central places, provided that each additional place has a population of at least 15,000 and that each has at least one-third the population of the most populous incorporated place. If the UA does not contain any incorporated place of 2,500 or more, the larg- est CDP is selected as the central place, provided that more than 50 percent of its population is located outside the boundaries of a military installation.
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In all instances, the entire entity is classified as a central place. Extended cities are an exception—only their urban portions are classified as central. There is no limit on the number of central places in a UA; however, not all central places are necessarily included in the UA title.
Assignment of UA Titles The title of a UA identifies those places that are most important within the UA; where appropriate, it links the UA to the encompassing MA. If a single MA encompasses most of the UA, the title of the UA generally is the same as the title of the MA.
The title of a UA generally is different from any MA title when:
- Most of the UA is not part of a single MA.
- The UA does not include any place that is a central city of the encompassing MA.
- The UA is not located in an MA. In these instances, the Census Bureau uses the total population of the central places included in the UA—with a preference for incorporated places—to determine the UA title. The name(s) of the State(s) in which the UA is located is (are) always part of the UA title.
A regional title may be used to identify a UA with a population of one mil- lion or more where such a name provides an unambiguous description of the area. Regional titles include only the name of the largest city in the UA, followed by the regional reference; for example: Chicago-Northwestern Indiana and New York-Northeastern New Jersey.
The MA central cities and titles used to determine UA central places were those that were in effect on June 30, 1990. Even though the MA central cities, titles, and geographic components underwent a later review and revision by the OMB based on the 1990 census results, such revisions did not affect the central places, titles, or boundaries of UAs already defined. (For information on how UAs delineated during the intercensal period may affect MAs, see the “Intercensal MA Changes” section in Chapter 13.)
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Classification as Urban or Rural For UAs that qualified in earlier censuses, the 1990 delineation process began at the previous (usually 1980) UA boundary. In the case of potential UAs, the boundary of the central place(s) was the starting point for exam- ining territory to determine qualification. Portions of surrounding territory were added to the core if they had a population density of at least 1, people per square mile, or if they could be included through recognition of a whole place, an extended city, a jump, a nonresidential urban land use area, or by virtue of being undevelopable territory (see previous section).
For making specific delineation decisions, the Census Bureau frequently relied on small geographic entities called analysis units (AUs). Each AU consisted of either a single census block or—more frequently—a cluster of contiguous blocks, often of similar physical size and shape. An AU generally represented a single housing cluster, other territory having a closely spaced street pattern, or territory having a similar population density or land use.
The Census Bureau established AUs to decide what pieces of territory to include or exclude. Staff used the automated system to measure and evaluate the following kinds of areas as AUs: core areas of places, outly- ing clusters of high-density blocks, gaps in the pattern of continuous development (usually potential jumps), urban and rural components of extended cities, indentations, and enclaves. In all these situations, the grouping of blocks into AUs established an interpretative grid of small- area geographic units. The census blocks within each AU eventually were classified as either urban or rural.
Delineation Results for 1990 After the determination of UA boundaries, there followed the separa- tion or merger of contiguous UAs and the determination of UA central places and titles. Ultimately, the Census Bureau recognized 405 UAs for the 1990 census—396 in the United States and 9 in Puerto Rico. In addi- tion, the Census Bureau recognized 4,019 urban places outside of UAs—
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3,938 in the United States and 81 in Puerto Rico and the Outlying Areas. Of the 280 extended cities that the Census Bureau identified in the United States (none in Puerto Rico and the Outlying Areas), 128 were located inside UAs and 152 outside of UAs.
Geographic Relationships and Patterns
Places, Nonplace Territory, and Population Density The use of places as geographic building blocks often has an effect on the size, shape, and extent of a UA, especially where the UA consists mostly of places. Incorporated places and CDPs frequently contain low-density areas (less than 1,000 people per square mile) that would not qualify for inclusion in the UA had the territory been outside of any place. Therefore, a UA whose urban fringe consists mostly of places may include more sparsely settled territory than a UA whose fringe contains mostly nonplace territory. As a result, the urban fringe of a UA consisting mostly of places often has a lower population den- sity than a UA whose urban fringe is mostly nonplace territory.
Metropolitan Areas Since 1980, UAs have been used as one of the criteria for designating an area as metropolitan. A UA also can play a role in determining the geographic extent of an MSA or CMSA. In general, a UA represents the densely settled portion of an MA, and nearly every MSA/CMSA contains at least one UA at its core. The UAs generally cover much smaller geographic areas than do MAs and have much higher average population densities.
Two or more UAs may exist within a single MA. Conversely, a UA may extend into more than one MA or into nonmetropolitan area; some UAs are located entirely outside metropolitan areas.
Other Geographic Entities The urban and rural classifications may be applied to many of the geo- graphic entities recognized by the Census Bureau (refer to Figure 2-
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The following series of publications contain data for UAs and for summary geographic areas such as urban and rural: CPH-1 Summary Population and Housing Characteristics CPH-2 Population and Housing Unit Counts CPH-5 Summary Social, Economic, and Housing Characteristics CP-1 General Population Characteristics CP-2 Social and Economic Characteristics CH-1 General Housing Characteristics CH-2 Detailed Housing Characteristics
The CPH-2 series, which consists of separate reports for each State or sta- tistically equivalent entity, provides urban and rural information and data for all UAs along with their component places and county subdivisions. Each report contains one or more page-size maps to show the extent of each UA located entirely or partially in that State. These individual area UA Outline Maps show (1) the UA boundaries; (2) the boundaries and names of States, counties, county subdivisions (MCDs, CCDs, and other entities), and places; and (3) selected base map features such as major water bodies. The map scale is four miles to the inch.
All report series listed above include a summary report for the entire Nation; for example, CPH-1-1, Summary Population and Housing Charac- teristics/United States. These initial reports contain many tables that pre- sent data by UA, central place or places, and urban fringe; the following tabular format is used: All Persons Land Area (sq. mi.) Persons (per sq. mi.)
Albany, GA ........................ 87,223 71.4 1221. In central place ............ 78,122 55.5 1407. Albany City, GA ...... 78,122 55.5 1407. Urban fringe ................ 9,101 15.9 572.
Where UAs extend across State boundaries, there are data summaries both for the State parts and for the whole UA. Each United States sum- mary report contains a two-page map, “Urbanized Areas of the United States: 1990,” which shows the names and locations of all UAs nationwide.
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No other report series contain data on UAs, although all contain summaries for urban and rural population and housing data. However, the following individual nationwide reports, sometimes composed of multiple volumes, are devoted to UAs; each also contains the two-page UA summary map. CP-1-1C General Population Characteristics for Urbanized Areas (100-percent data) CP-2-1C Social and Economic Characteristics for Urbanized Areas (mostly sample subjects) CH-1-1C General Housing Characteristics for Urbanized Areas (100-percent data) CH-2-1C Detailed Housing Characteristics for Urbanized Areas (generally sample subjects) For the 1990 UA program, the Census Bureau produced a two-volume sup- plementary report, CPH-S-1-2, Urbanized Areas of the United States and Puerto Rico, containing UA tables and maps that appear in the separate State reports of the CPH-2 series. 10
Computer Tape Files and CD-ROMs The Census Bureau’s Summary Tape Files (STFs) and other machine-read- able data products provide statistics with greater subject-matter detail than is shown in the printed reports. Each STF presents a particular set of data tables for specific types of geographic entities, with further subdivision into three or more file types (indicated by a letter suffix). The following STFs provide data for UAs and for urban and rural categories:
STF 1B 100-percent data for the full geographic hierarchy to block level STF 1C 100-percent data for UAs, urban and rural (summaries by State) STF 2C 100-percent data for UAs, urban and rural (summaries by State) STF 3A Sample data for UAs, urban and rural STF 3C Sample data for UAs STF 4B Sample data for urban and rural (summaries by State) STF 4C Sample data for UAs, urban and rural (summaries by State) The STFs 1B, 1C, 3A, and 3C also are available in compact disc—read-only memory (CD-ROM) format.
