A congressional district is an electoral constituency that elects a single member of a congress. Countries with congressional districts include the United States, the Philippines, and Japan. A congressional district is based on population, which, in the United States, is taken using a census every ten years.
There are 435 congressional districts in the United States House of Representatives, with each one representing approximately 711,000 people. In addition to the 435 congressional districts, the five inhabited U.S. territories and the federal district of Washington, D.C. each send a non-voting delegate to the House of Representatives. The Census Bureau within the United States Department of Commerce conducts a decennial census whose figures are used to determine the number of Representatives that each state sends to Congress, and therefore the number of congressional districts within each state. The borders of those districts are set by the states, and within each state all districts are required to have approximately equal populations (see Wesberry v. Sanders). The 2012 elections were the first to be based on the congressional districts which were defined based on the 2010 Census data.