Election Research: Subject Guide: Districting Info and Maps

The U.S. Census Bureau is required to take a census of population every ten years, during the year ending with zero. According to the Constitution of the United States, this decennial census has one fundamental purpose: to ensure that number of seats each State has in the U.S. House of Representatives reflects the relative size of the State's population as compared with other States. Currently there are 435 representatives divided among the 50 States. Each of these representatives is elected by the voters of a congressional district, defined as an area established by law for the election of representatives to the U.S. Congress. Each congressional district is to be as equal in population to all other congressional districts in the State as practicable, based on the decennial census counts. The number of congressional districts in each State can change after a decennial census. After the number of seats assigned to the individual States is determined (apportionment), the task of drawing the new congressional districts (redistricting) is generally given to each State legislature. (Text from nationalmap.gov)