Geography

States

States are the primary governmental divisions of the United States. The Census Bureau also recognizes the District of Columbia as a state equivalent in the economic census. The Island Areas (which include Puerto Rico, the U.S. Virgin Islands, Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands) are also identified in selected data elements in Rural Data Central.

Counties (or Statistically Equivalent Entities)¹

The primary legal divisions of most states are termed “counties.” In Louisiana, these divisions are known as parishes. In Alaska, which has no counties, the statistically equivalent entities are census areas, cities and boroughs (e.g., Juneau City and Borough), municipalities (e.g., Anchorage), and organized boroughs. Census areas are delineated cooperatively for data presentation purposes by the state of Alaska and the U.S. Census Bureau. In four states (Maryland, Missouri, Nevada, and Virginia), there are one or more incorporated places that are independent of any county organization and thus constitute primary divisions of their states; these incorporated places are known as ‘‘independent cities’’ and are treated as equivalent to counties for data presentation purposes. Municipios are the primary legal divisions of Puerto Rico. For data presentation purposes, the U.S. Census Bureau treats a municipio as the equivalent of a county in the United States. There are 78 municipios in Puerto Rico, all of which are functioning governmental entities. The District of Columbia has no primary divisions, and the entire area is considered equivalent to a county for data presentation purposes.

Census Tracts²

Census Tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity that are updated by local participants prior to each decennial census as part of the Census Bureau’s Participant Statistical Areas Program. The Census Bureau delineates census tracts in situations where no local participant existed or where state, local, or tribal governments declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of statistical data.

Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. A census tract usually covers a contiguous area; however, the spatial size of census tracts varies widely depending on the density of settlement. Census tract boundaries are delineated with the intention of being maintained over a long time so that statistical comparisons can be made from census to census. Census tracts occasionally are split due to population growth or merged as a result of substantial population decline.

Census tract boundaries generally follow visible and identifiable features. They may follow nonvisible legal boundaries, such as minor civil division (MCD) or incorporated place boundaries in some states and situations, to allow for census-tract-to-governmental-unit relationships where the governmental boundaries tend to remain unchanged between censuses. Census tracts are nested within state and county boundaries in the standard census geographic hierarchy.

Congressional Districts

The 50 states are divided into 435 congressional districts which represent the service areas for all voting members of the U.S. House of Representatives. The decennial census population count determines the distribution, among states, of these 435 congressional districts while the states themselves determine each congressional district’s specific geographic boundaries. In each state, congressional districts must be “as equal in population … as practicable”³ and comport with the state laws and court orders used in creating them. Congressional districts’ boundaries nest within states but intersect county and census tract boundaries. Every ten years, after the conclusion of the decennial census, congressional districts are updated.

Tribal Tracts

Tribal census tracts are the smallest geographic subdivisions of reservation and off-reservation trust land (“American Indian land”). Tribal census tracts relate to federally recognized American Indian land and do not nest within state, county, or census tract boundaries. Like census tracts, tribal census tracts have an optimum population of 4,000, use visible features for boundaries, and are defined mostly by local governments. There were 492 tribal census tracts as of 2019.⁵

Continuums of Care

HUD’s continuum of care areas (“Continuum of Care” or “CoC” geography) represent the service areas for “regional or local planning bodies that coordinate housing services funding for homeless families and individuals.”⁶ CoC areas exist in all 50 states, Washington, DC, and Puerto Rico. CoC areas, reflecting differences in planning body service areas, can be based on different geographies such as a single city, a city and surrounding county, a region, or a state. CoCs can also change periodically depending on the underlying planning body.⁷

NOTES

¹ “Glossary – County or Statistically Equivalent Entity,” U.S. Census Bureau, April 11, 2022,
https://www.census.gov/programs-surveys/geography/about/glossary.html#par_textimage_12.

² “Glossary – Census Tracts” U.S. Census Bureau, April 11, 2022,
https://www.census.gov/programs-surveys/geography/about/glossary.html#par_textimage_13.

³ “About Congressional Districts,” U.S. Census Bureau, October 8, 2021,
https://www.census.gov/programs-surveys/geography/guidance/geo-areas/congressional-dist.html

⁴ “Decoding State-County Census Tracts Versus Tribal Census Tracts,” U.S. Census Bureau, July 17, 2012,
https://www.census.gov/newsroom/blogs/random-samplings/2012/07/decoding-state-county-census-tracts-versus-tribal-census-tracts.html

⁵ “Tallies [Census Geographies],” U.S. Census Bureau, July 18, 2022,
https://www.census.gov/geographies/reference-files/time-series/geo/tallies.html.

⁶ “What is a Continuum of Care?,” National Alliance to End Homelessness, January 14, 2010,
https://endhomelessness.org/resource/what-is-a-continuum-of-care/.

⁷Zack W. Almquist, Nathaniel E. Helwig, and Yun You, “Connecting Continuum of Care Point-in-Time Homeless Counts to United Census Areal Units,” Mathematical Population Studies, 27, no. 1 (2020), pages 46-58.