The US census was established largely for the purpose of determining the reapportionment of legislative districts. As population shifts around the country congressional seats are taken from cities of declining population and added to those where population has grown.

The gathering of data has become cause for significant political debate with regard to the 2000 census. Democrats feel that previous censuses have grossly undercounted urban populations and so have unfairly taken seats away from areas where the electorate has tended to vote for them. As a result, they wish to institute sampling techniques to compensate for any potential undercount. Republicans, whether or not they agree that an undercount has occurred, are happy with traditional census-gathering techniques.

Further debates have occurred over the establishment of districts to allow for or limit minority representation. A state in the South with a large African American population may nevertheless elect few black Congress members due to the way districts are drawn.

In 1982 efforts were made to change this when the Voting Rights Act was amended to require certain jurisdictions to take steps to give minority voters an opportunity to elect candidates of their choice. However, first attempts to accomplish this by making constituencies out of dispersed populations have been declared unconstitutional “racial gerrymanders” by the Supreme Court.