Redistricting, a form of redistribution, is the process of changing of political borders in the United States. This often means changing electoral district and constituency boundaries, usually in response to periodic census results. This takes place by law or constitution at least every decade in most representative democracy systems using first-past-the-post or similar electoral systems to prevent geographic malapportionment.
In 36 states, the state legislature has primary responsibility for creating a redistricting plan, in many cases subject to approval by the state governor. To reduce the role that legislative politics might play, 5 states (Arizona, Hawaii, Idaho, New Jersey and Washington), carry out congressional redistricting by an independent, bipartisan commission. Iowa and Maine give independent bodies authority to propose redistricting plans, but preserve the role of legislatures to approve them. Seven states have only a single representative for the entire state because of their low populations; these are Alaska, Delaware, Montana, North Dakota, South Dakota, Vermont and Wyoming. The state constitutions and laws also mandate which body has responsibility over drawing the state legislature boundaries. In addition, those municipal governments that are elected on a district basis (as opposed to at-large) also redistrict.
Each state has its own standards for creating Congressional and legislative districts. In addition to equalizing the population of districts and complying with Federal requirements, criteria may include attempting to create compact, contiguous districts, trying to keep political units and communities within a single district, and avoiding the drawing of boundaries for purposes of partisan advantage or incumbent protection. In the states where the legislature (or another body where a partisan majority is possible such as IL or OH) is in charge of redistricting, the possibility of gerrymandering (the deliberate manipulation of political boundaries for electoral advantage, usually of incumbents or a specific political party) often makes the process very politically contentious, especially when the two houses of the legislature, or the legislature and the governor, are from different parties. The state and federal court systems are often involved in resolving disputes over Congressional and legislative redistricting when gridlock prevents redistricting in a timely manner. In addition, the losers to an adopted redistricting plan often challenge it in state and federal courts. Justice Department approval (which is known as preclearence) is required under Section 5 of the Voting Rights Act of 1965 in certain states that have had a history of racial barriers to voting.
Partisan domination of state legislatures and improved technology to design contiguous districts that pack opponents into as few districts as possible have led to district maps which are skewed towards one party. So many states (including Texas, Michigan, Pennsylvania, Florida, Georgia and Maryland) have succeeded in removing competition for most House seats in those states that it has deadened competition for House seats nationally. Other states (New York, New Jersey, California) have opted to protect incumbents of both parties, again reducing the number of competitive districts. The Supreme Court's ruling on the Pennsylvania gerrymander in Vieth v. Jubelirer effectively cemented the right of elected officials to choose their constituents, and it is up to a small number of competitive districts in a small number of states to determine majority control of Congress, since each party has about 190 districts which have very little likelihood of changing party control. The 2003 redistricting in Texas and the mid-decade redistricting in Georgia established the precedent of allowing the majority party in state governments to redraw the boundaries to favor the election of the majority-party candidates in subsequent elections.