In 28 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, twelve states (Alaska, Arizona, California, Colorado, Hawaii, Idaho, Missouri, Montana, New Jersey, Ohio, Pennsylvania, and Washington) determine congressional redistricting by an independent or bipartisan redistricting commission. Five states: Maine, New York, Rhode Island, Vermont, and Virginia give independent bodies authority to propose redistricting plans, but preserve the role of legislatures to approve them. Arkansas has a commission composed of its governor, attorney general, and secretary of state. 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.
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) 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 majorities of 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 pre-clearance) was formerly 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. Consequently, many states including Florida, Georgia, Maryland, Michigan, Pennsylvania and Texas have succeeded in reducing or effectively eliminating competition for most House seats in those states. In 2003 Republicans in Texas increased their representation in the U.S. House through a controversial mid-decade redistricting.
Other states including California, New Jersey and New York have opted to protect incumbents of both parties, again reducing the number of competitive districts. The Supreme Court's ruling on the Pennsylvania gerrymander effectively cemented the right of elected officials to select their constituents by eliminating most of the grounds for disenfranchised constituents to challenge gerrymandered lines.
Redistricting has to follow certain criteria to be accepted.
Gerrymandering is the practice of drawing district lines to achieve political gain for legislators. The practice of gerrymandering involves the manipulation of district drawing in aims to leave out, or include, specific populations in a legislator's district to ensure his/her reelection.