Tracts are regions of U.S. census geography that originated as analogs of urban neighborhoods. They retain some of that purpose today, and for that reason, tract limits are partially defined by population characteristics in addition to political boundaries and population. Tracts are preferable to other regions because the tabulations are more complete than those of smaller areas and are more easily compared than wards, zip codes, or other administrative regions not defined by population.

First proposed in 1906 by the demographer Walter Laidlaw, census tracts were intended to be a permanent framework to simplify tracking demographic changes. Although the census bureau agreed in principle to provide tract-level tabulations for eight cities in 1910, there was no immediate interest outside New York City. Demand had grown enough ...