U.S. Census Resources on the Web
1990 Census of Population & Housing
Geography Terms

Census reports are organized by different geographic hierarchies, i.e. groupings of geographic units. The units may be based on political divisions (states, counties, American Indian reservations, etc.) or population size or density. With some geographic hierarchies, you can get both 100%-count (STF1) and sample data (STF3); for others (like ZIP codes) you can only get 100%-count data (STF1).

The following guide illustrates the most common geographic hierarchies and groupings. Definitions of the terms related to that hierarchy follow each chart. The definitions are quite broad. For more precise definitions, please see the documentation for the Census report/product you're using.

Jump to: Standard hierarchy | Hierarchy for retrieving tract/BNA or block group data |
Metropolitan areas | Urban-rural | American Indian reservations | Congressional districts | Zip codes

The standard geographic hierarchy (from largest division to smallest)

United States: includes the 50 states, the District of Columbia, and outlying areas (American Samoa, Guam, the Northern Mariana Islands, Palau, Puerto Rico, and the Virgin Islands).

Region: the Census divides the U.S. into four regions: Northeast, Midwest, South, West.

Division: regions are further divided into a total of nine divisions (rarely used in reports).

State: the primary governmental divisions of the United States.

County: the primary political divisions of most states, including Wisconsin.

County equivalent: geographic entity not legally referred to as a county but treated as such for data tabulation purposes (example: parishes in Louisiana).

County subdivisions: primary subdivision of counties and their equivalents for the reporting of decennial census data. The most common county subdivisions are:
  • Minor civil divisions (MCDs): the primary political or administrative divisions of a county. MCDs represent many different kinds of legal entities with a wide variety of governmental and/or administrative functions. MCDs include, among others, American Indian reservations, assessment districts, boroughs, precincts, towns, and townships.
Other county subdivisions include:
  • Census county divisions (CCDs): subdivisions of a county where minor civil divisions (MCDs) are not established or change frequently. Defined by Census and local officials for statistical purposes. CCDs have no legal functions, and are not governmental units.
  • Census subareas: statistical subdivisions of census areas (Alaska only) and boroughs.
  • Unorganized territories: in nine states (AR, IA, KS, LA, ME, MN, NC, ND, and SD), some counties contain territory that is not included in an MCD recognized by the Census Bureau. Each separate area of unorganized territory in these States is recognized as one or more separate county subdivisions for census purposes.

Place: includes incorporated places and census designated places (CDP).
  • Incorporated places: legally incorporated cities, boroughs, towns, or villages (with some exceptions, depending on the state). In Wisconsin, incorporated places include cities and villages, not towns (towns are considered minor civil divisions).
  • Census designated places (CDPs): densely settled concentration of population that are identifiable by name, but are not legally incorporated places. For decennial census purposes, the statistical counterparts of incorporated places.

Census tract: statistical subdivision of a Metropolitan Area or other densely populated county. Defined by local committees. Census tracts usually have between 2,500 and 8,000 persons. The spatial size of census tracts varies widely depending on the density of settlement.

Block numbering area (BNA): small statistical subdivision of a county for grouping and numbering blocks in non-metropolitan counties.

Block group (BG): group of blocks within a census tract or block numbering area (BNA). BGs generally contain between 250 and 550 housing units, with the ideal size being 400 housing units.

Block: small area bounded on all sides by visible features such as streets, roads, streams, and railroad tracks, and by invisible boundaries such as city, town, township, and county limits and property lines. The entire country was "blocked" for the 1990 Census. (Sample data not available for blocks.)

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Hierarchy to use when retrieving tract/BNA or block group data from online sources

See previous section for definitions.

Web sites with tract data

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Metropolitan areas (MAs) and their relatives-MSAs, CMSAs, PMSAs

Metropolitan Area (MA): large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus.
MAs are either:

For each MSA & CMSA, there is a
  • Central City: the largest place and, in some cases, additional places.

Metropolitan area (MA): a large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus.
  • Some are defined around two or more nuclei.
  • Each MA must contain either a place with a minimum population of 50,000 or a Census Bureau-defined urbanized area and a total MA population of at least 100,000 (75,000 in New England).
  • An MA comprises one or more central counties, and also may include one or more outlying counties that have close economic and social relationships with the central county.
  • In the Census, MAs are designated either Metropolitan Statistical Areas (MSAs) or Consolidated Metropolitan Statistical Areas (CMSAs).

Central City: in each MSA and CMSA, the largest place and, in some cases, additional places are designated as "central cities" under the official standards.

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Urban-rural hierarchy

Used with other hierarchies. For example, the concepts of "urban" and "rural" are used in reports for both the Metropolitan Area hierarchy and the Standard hierarchy.

Urban: comprising all territory, population, and housing units in urbanized areas and in places of 2,500 or more persons outside urbanized areas.
  • Urbanized Area (UA): one or more places ("central place") and the adjacent densely settled surrounding territory ("urban fringe") that together have a minimum of 50,000 persons.
    • Urbanized Area Central Place: one or more central places function as the dominant centers of each UA.
    • Urban Fringe: densely settled territory adjacent to a central place. The urban fringe generally consists of contiguous territory having a density of least 1,000 persons per square mile.
  • Urban Places Outside UAs: Incorporated places and Census-designated places of 2,500 or more outside UAs

Rural: territory, population, and housing units not classified as urban.
In the 100% data products, "rural" is divided into:
  • "Places of less than 2,500"
  • "Not in places:" comprises "rural" outside incorporated and census designated places and the rural portions of extended cities.
In the sample data products, "rural" is subdivided into:
  • "Rural farm:" all rural households and housing units on farms (places from which $1,000 or more of agricultural products were sold in 1989)
  • "Rural nonfarm:" the remaining rural

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Other geographic divisions

American Indian Reservations

Federal American Indian reservations: areas with boundaries established by treaty, statute, and/or executive or court order, and recognized by the Federal Government as territory in which American Indian tribes have jurisdiction. May cross state, county, county subdivision, and place boundaries.

State reservations: lands held in trust by State governments for the use and benefit of a given tribe. The names of American Indian reservations recognized by State governments, but not by the Federal Government, are followed by "[State]." May cross county, county subdivision, and place boundaries.

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Congressional Districts

The 435 areas from which persons are elected to the U.S. House of Representatives. Both sample and 100%-count data available for 103rd & 104th Congress districts.

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Zip Codes

Postal zip codes identified for mail delivery, rather than physical location, as of April 1990. Many zip codes changed as a result of the 1990 Census, but those changes are not reflected in the 1990 Census of Population. (Sample data only available)

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Page created on 11/2/99; last updated on 4/10/01.

Created and maintained by:

Beth Harper
Government Documents Reference Librarian
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