Census Tracts, Blocks, & Block Groups (plus other Census definitions)
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. (See Census Overview for a list of 100 percent topics and those that are only available in the 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.
Definitions of other terminology used in the census:
- Definitions of terms Census terms can be found on the page entitled Definition and Explanation of Terms.
- Overview of Race and Hispanic Origin 2010 is recommended reading for everyone who intends to use Census data. 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.