Image from U.S. Census Bureau, Wikimedia Commons, public domain
The United States Constitution mandates a census every ten years to determine how many seats each state will have in the U.S. House of Representatives. The U.S. Census Bureau, with oversight from Congress, is responsible for planning and conducting the census, and reporting the results.
Definition for Census Tract (From American FactFinder, U.S. Census Bureau)
A small, relativiely permanent statistical subdivison of a county delinated by a local committee of census data used for the purpose of presenting data. Census tract boundaries normally follow visible features, but may follow governmental unit bountaries and other non-visible features in some instances; they always nest within counties. Designed to be relatively homogeneous units with respect to population characteristics, economic status, and living conditions at the time of establishment, census tracts average about 4,000 inhabitants. They may be split by any sub-county geographic entity. Census tract boundaries never cross county lines.
Geographic regions defined for census purposes (largest to smallest areas):
See Geographic Terms and Concepts - Census Tract (U.S. Census Bureau)
See Tracts and Block Numbering Areas (U.S. Census Bureau)
