Systems of single member and proportional representation are very different. Single member representation, as in the United States, works by carving every state in the country into individual districts based upon population density. In the United States, the number of one-half of a million people is the rough number of citizens in each district. As states lose population for any reason, such as a major decline in job opportunities to other states, they lose voting districts. The number of districts and, consequently, the number of elected officials in the House of Representatives (under the U.S. Constitution, each state has two senators) representing each state is determined on the basis of the national census taken every ten years. Populations shifts, therefore, determine which regions gain and which regions lose representation.
