Since a single party usually controls each state legislature, it is in the best interest of the party in power to redistrict their state so that their party will have more seats in the House than the opposition party. This manipulation of electoral districts is known as gerrymandering. Although illegal, gerrymandering is the process of modifying congressional districts to benefit the party in power.
The term gerrymandering is derived from Elbridge Gerry (1744-1814), the governor of Massachusetts from 1810 to 1812. In 1812, Governor Gerry signed a bill into law that redistricted his state to overwhelmingly benefit his party, the Democratic-Republican Party. The opposition party, the Federalists, were quite upset.
One of the congressional districts was shaped very strangely and, as the story goes, one Federalist remarked that the district looked like a salamander. No, said another Federalist, it's a gerrymander. The Boston Weekly Messenger brought the term gerrymander into common usage when it subsequently printed an editorial cartoon that showed the district in question with a monster's head, arms, and tail and named the creature a gerrymander.
Governor Gerry went on to become vice president under James Madison from 1813 until his death a year later. Gerry was the second vice president to die in office.
Gerrymandering, which had taken place prior to the coinage of the name and continued for many decades thereafter, has been challenged many times in federal courts and has been legislated against. In 1842, the Reapportionment Act required that congressional districts be contiguous and compact. In 1962, the Supreme Court ruled that districts must follow the principle of "one man, one vote" and have fair borders and an appropriate population mixture. Most recently, the Supreme Court ruled in 1985 that manipulating district borders to give an advantage to one political party was unconstitutional.
There are three techniques used to gerrymander districts. All involve creating districts that have a goal of encompassing a certain percentage of voters from one political party.
The first method is called the "excess vote." It is an attempt to concentrate the voting power of the opposition into just a few districts, to dilute the power of the opposition party outside of those districts that contain an overwhelming majority of the opposition's voters.
The second method is know as the "wasted vote." This method of gerrymandering involves diluting the voting power of the opposition across many districts, preventing the opposition from having a majority vote in as many districts as possible.
Finally, the "stacked" method involves drawing bizarre boundaries to concentrate the power of the majority party by linking distant areas into specific, party-in-power districts.
The process of reapportionment (to divide the 435 seats in the House of Representatives into the fifty states) takes place soon after every decennial census (the next will be 2010). Since the primary purpose of the census is to count the number of residents of the United States for purposes of representation, the Census Bureau's highest priority is to provide data for redistricting. Basic data must be provided to the states within one year of the Census - April 1, 2011.
Computers and GIS were utilized in the 1990 and 2000 Census by the states to make redistricting as fair as possible. Despite the use of computers, politics does get in the way and many redistricting plans are challenged in the courts, with accusations of racial gerrymandering tossed about.
We certainly won't expect accusations of gerrymandering to vanish anytime soon.
The U.S. Census Bureau's Redistricting site provides additional information about their program.