Effect
Gerrymandering is effective because of the wasted vote effect. By packing opposition voters into districts they will already win (increasing excess votes for winners) and by cracking the remainder among districts where they are moved into the minority (increasing votes for eventual losers), the number of wasted votes among the opposition can be maximized. Similarly, with supporters holding narrow margins in the unpacked districts, the number of wasted votes among supporters is minimized.
While the wasted vote effect is strongest when a party wins by narrow margins across multiple districts, gerrymandering narrow margins can be risky when voters are less predictable. To minimize the risk of demographic or political shifts swinging a district to the opposition, politicians can create more packed districts, leading to more comfortable margins in unpacked ones.
| Examples of gerrymandered districts |
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North Carolina's 12th congressional district An example of packing. The district has predominantly African-American residents who vote for Democrats.
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Designed to proportionally segment voters of the Democratic Party, California's 23rd congressional district, is confined to a narrow strip of coast, an example of the packing style of districting.
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An example of "cracking" style of gerrymandering. The urban (and mostly liberal Democratic) concentration of Columbus, Ohio, located at the center of the map in Franklin County, is split into thirds, each segment attached to—and outnumbered by—largely conservative suburbs that vote Republican.
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California's 11th congressional district drawn to favor its then-Republican incumbent.
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Bi-partisan incumbent gerrymandering produced California District 38, home to Grace Napolitano, a Democrat, who ran unopposed in 2004.
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Texas' controversial 2003 partisan gerrymander produced Texas District 22 for former Rep. Tom DeLay, a Republican.
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The odd shapes of California Senate districts in Southern California (2008) have led to claims of gerrymandering.
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The earmuff shape of Illinois's 4th congressional district packs two Hispanic areas while retaining narrow contiguity along Interstate 294.
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After the Democrat Jim Matheson was elected in 2000, the Utah legislature redrew the 2nd congressional district to favor future Republican majorities. The predominantly Democratic city of Salt Lake was connected to predominantly Republican eastern and southern Utah through a thin sliver of land running through Utah County. But, Matheson continued to be re-elected. In 2011, the legislature created new congressional districts that combined conservative rural areas with more urban areas to dilute Democratic votes.
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Illinois' 17th congressional district in the western portion of the state is gerrymandered: the major urban centers are anchored and Decatur is included, although nearly isolated from the main district.
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