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Guide to the U.S. Census of Population: Definitions

This guide has been archived and may have outdated information or broken links.

Terminology used in the Census:

  • FAQ Definitions is a lengthy list of terms and definitions of census related terms. Use your browser's find on page search feature to locate a definition as the list is not in alphabetical order.
  • Definition and Explanation of Terms provides links to the specific glossaries of terms for the various statistics gathering programs of the U.S. Census Bureau.
  • Overview of Race and Hispanic Origin 2010 is recommended reading for everyone who intends to use Census data related to race and ethnicity. Note specifically that Hispanics and Latinos may be of any race as this may make a difference in which tables a specific user should select to find needed data and/or how to interpret the data that is found.

What is a Zip Code Tabulation Area (ZCTA)?

A ZIP Code Tabulation Area is a geographic area that approximates the delivery area for a five-digit or a three-digit (Census 2000 only) ZIP Code. The Census Bureau defines ZCTAs by allocating each block that contains addresses to a single ZCTA, and therefore ZCTAs do not precisely depict the area within which mail deliveries associated with that ZIP Code occur. For the 2010 Census ZCTAs no longer have nationwide coverage and better approximate the associated five-digit ZIP Code for an area. More information

What is a Census Tract?

A census tract is a small statistical subdivision of a county. Census tract data allows a user to find population and housing statistics about a specific part of an urban area from both 100-percent data and sample data. Census tracts are particularly important when you want information about part of a city, such as Northridge or other communities in the San Fernando Valley which are part of the City of Los Angeles. A single community may be composed of several census tracts; there may be hundreds of census tracts in a large city.

What is a Census Block?

A census block is a subdivision of a census tract. In Census 2010, a census block is the smallest geographic unit for which the Census Bureau tabulates 100-percent data such as Age, Hispanic or Latino Origin, Race, Sex, Household Relationship, and whether Homeowners or Renters. Many census blocks correspond to individual city blocks bounded by streets, but this is not always true; blocks - especially in rural areas - may include many square miles and may have some boundaries that are not streets.

What is a Block Group?

In Census 2010, a block group is part of a census tract. A census tract may have one or more block groups within it; a block group usually consists of several census blocks within the same tract. So, a block group is geographically smaller than a census tract, but larger than a census block. A block group is the smallest geographic unit for which the Census Bureau tabulates sample data. (That means statistics based on sample data--statistics about income, education, citizenship, etc.--are only available for block groups and larger geographies; sample data is not available for a census block). A block group consists of all the blocks within a census tract with the same beginning number.