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. 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.
U.S. Census Bureau, Geography Division. Geographic Terms and Concepts – Census Tract
Changes in census tracts: Changes are made to the boundaries of census tracts with each decennial census.
Data presented by census tracts in IECAM: IECAM does not present data by census tracts in its online database. However, IECAM sometimes uses census tract data to make estimates for special purposes.