Redistricting should be a way of ensuring your vote counts. If all districts have roughly the same number of people in them and are drawn to respect natural communities — neighborhoods where people share a heritage, work in the same industry, or just generally feel tied to their neighbors — voters have a chance to be represented by politicians who represent their areas' collective interests.
To that end, states are required to redraw lines for districts, all the way from Congress to county boards of supervisors, every 10 years to reflect demographic changes.
But that's where theory meets the harsh reality. Instead of voters choosing politicians, redistricting at its worst lets politicians choose voters.
Communities can have their influence diluted or overly concentrated by line-drawers interested in partisan gain, limiting minorities' influence, or pleasing powerful interests. (See our earlier story, The Hidden Hands in Redistricting .) The right lines can all but guarantee an incumbent a decade's worth of electoral success, or alternatively can help send others into retirement.
Such shenanigans persist, despite the 1965 Voting Rights Act and subsequent legal decisions meant to limit them. Indeed, increased mapping technology and know-how have allowed for ever more subtle manipulation of district lines.
Here's a rundown of the realities of redistricting, and the terms used by critics and insiders alike:
Cracking: This technique splits a community into multiple districts to ensure it doesn't have significant sway with a candidate. In the ugly racial history of redistricting, cracking was often used to ensure that African-Americans could not elect African-American politicians. The Voting Rights Act banned racially motivated cracking, with some success. But cracking is still common, with the goal now frequently to fracture communities for partisan gain.
Austin: Texas Republicans, who control both the state legislature and the governor's office, approved very Republican-friendly congressional redistricting earlier this year. A case in point: liberal Austin, which the plan splits into six districts that radiate outward to encompass hundreds of miles of conservative suburban and rural territory. (The Justice Department recently moved in court to block the plan, but not because of cracking in Austin. Instead, the suit alleges, lawmakers tried deliberately to minimize the voices of minority voters. Lawyers defending the Texas plan  on behalf of the state say it protects Latino incumbents and creates additional Latino-friendly districts.)
Rochester area: In the 2000 redistricting cycle, slow population growth cost New York State two congressional seats. In a backroom deal, Republicans and Democrats agreed to eliminate one seat each. As part of the deal, the Democrat-friendly Rochester area was creatively sliced into multiple districts so it would be represented by one Republican and one Democrat.
The 28th District is a wide and narrow ribbon along Lake Ontario that incorporates parts of the Rochester area and Buffalo, 75 miles away, and is represented by Democratic Congresswoman Louise Slaughter. The 29th District lumps another piece of the Rochester area into an Appalachian mountain district that spans 100 miles south, represented by Republican Tom Reed. New York is still in the midst of its latest redistricting, and it's an open question whether the Rochester area will be made whole again.
Packing: When faced with too many unfriendly voters, it can also be a winning strategy to limit the damage by drawing them all into one district. The benefit for you is there are fewer of the voters you don't want in all the surrounding districts. When race is involved, redistricting pros call it bleaching.
Voters in the packed district often lose out because no matter how large their influence in the district, they can only have sway with one representative. If the community members were spread over more districts, and had significant population in each, they could have the ear of multiple politicians.
Orlando, Gainesville, Jacksonville: Florida's 3rd Congressional District scoops African-American neighborhoods out of three cities to form a district that has mostly swampland in between. Districts like this one, created in the 1990 redistricting cycle, helped African-American congressional candidates win historic victories. But the districts surrounding it are now much whiter, and thus more Republican, than ever before. Many credit the 1990 redistricting with turning Florida from a blue state to a red state.
Birmingham, Montgomery: At 62 percent African-American, the Alabama 7th Congressional District was already a safe minority district. But when the Republican-controlled state legislature redistricted this year, they extended the district's tendrils further into Birmingham and Montgomery to carve out African-American neighborhoods and create a 64 percent African-American district. The result: The surrounding districts now have almost no African-American voters. Previously competitive, the districts are now safely Republicans.
Hijacking: If there's an incumbent you don't like, you can make their re-election difficult by putting them in a district with another incumbent to contend with. If you don't like either incumbent in the newly drawn district, even better, because only one can be re-elected. If the two incumbents are from your rival party, you can force a costly primary battle, weakening your likely opponent before general election.
Cleveland, Toledo: Which brings us to the curious case of Reps. Marcy Kaptur and Dennis Kucinich. Ideological kindred spirits, friends, and now incumbents in the same oddly-shaped district. A district the Republican state legislature appears to have designed by drawing a straight line connecting the two representatives' homes, 110 miles apart, in Toledo and Cleveland. Republicans in Ohio's state legislature have defended the new district maps, saying they don't break any laws.
Kidnapping: Most politicians have geographic political bases; places they came up in politics where they have supporters, political allies, donors and name recognition. But what if their home address ends up in a different district than their base? That can make re-election tough, as North Carolina Congressman Brad Miller is about to find out. A new district boundary adopted by the state legislature there elegantly sweeps out to cut his home in Raleigh out of his old district. Republicans in the state have said that gaining congressional seats is a goal  of their redistricting effort.
Gerrymandering: Taken together, all of these handy techniques are known by this most famous redistricting term. In 1812, a Massachusetts governor named Eldridge Gerry was blamed for a redistricting plan designed to weaken the influence of the opposition Federalist party. The map, drawn to favor the Democratic-Republicans, included a long, squiggly district wrapped around the other districts like a salamander. The district, immortalized by a famous political cartoon, was dubbed the "gerry-mander."  (This was not fair to Gerry, since he was was not actually responsible for the map.) Gerrymandering has become the term of choice for all misbehavior in redistricting, but particularly refers to districts drawn in bizarre, wandering shapes for the benefit of particular politicians. A special subset of this is the sweetheart gerrymander, where incumbents of different parties collude to draw districts that make sure everyone stays in office.
Correction, November 2, 2011: An earlier version of this story stated that the City of Rochester was split into multiple districts. In fact, the city proper is entirely encompassed in the 28th congressional district. The urban area as defined by the U.S. Census, however, is split into four districts. This post has been updated accordingly.