Gerrymandering has been part of the political landscape for over 200 years. Yet, many people do not fully understand what it is and it is often difficult to explain.
The chart above was adapted by The Washington Post from a similar one that was posted to Reddit back in 2015. This chart provides a simple, more visual way to understand the process of gerrymandering. But, for those of you into the historical aspects of politics, I have provided a more detailed explanation based on material provided by Andrew Prokop on Vox.com
What is gerrymandering? 
In the US, every state elects a certain number of people to the House of Representatives — a number that’s based on the Census count of the state’s population. Pennsylvania, for instance, elects 18 House members. So Pennsylvania has to be divided into 18 congressional districts with roughly equal populations. In most US states, this process is controlled by the majority party in the state legislature.
Partisan gerrymandering occurs when this map-drawing process is intentionally used to benefit a particular political party — to help that party win more seats in the legislature, or more easily protect the ones it has. The goal is to create many districts that will elect members of one party, and only a few that will elect members of the opposite party. You can see Pennsylvania’s Congressional district map below.
You’ll notice that’s not a very structured map. Instead of it being filled with standard polygons, quadrilaterals and squares, it is full of jagged, irregular shapes. This was done intentionally. The map was drawn by Pennsylvania’s Republicans in 2010 to provide an advantage to their party in terms of the congressional elections. Although the Democrats won the state’s popular vote in 2012, Pennsylvania sent more Republicans (red) than Democrats (blue) to Congress (see map below).
Even though the House Republicans won only 49 percent of Pennsylvania’s popular vote, they won 72 percent of its House seats. And in 2014, the party breakdown of the state’s House seats stayed exactly the same.
Gerrymandering can affect any legislative body that has to have districts drawn — which includes both the US House of Representatives, and every state legislature. And since political power is at stake, fights over redistricting are long, loud and contemptuous.
The term gerrymandering is also sometimes used to describe somewhat different redistricting scenarios. Racial gerrymandering can mean the dilution of the voting power of certain racial or demographic groups, which is usually entangled with seeking partisan advantage. And a bipartisan gerrymander is a redistricting meant to protect incumbents of both parties.
Where does the term gerrymandering come from? 
The gerrymander is named after early 19th-century Massachusetts Gov. Elbridge Gerry (photo, right). After Gerry took office in 1810, his Democratic-Republican party redrew the map of the state’s Senate districts in a particularly dramatic and unusual manner. The aim was to weaken the opposing Federalist Party as much as possible.
The new map of the state’s Senate districts was widely mocked in the press, as in the cartoon below. One strangely shaped district was said to look like a salamander, and was combined with the governor’s name to create the term gerrymander.
According to Christopher Klein of the Boston Globe, Gov. Gerry was actually barely even involved in the map-drawing process, though he did sign the new map into law. But the press and the opposition Federalist Party trained their fire on Gerry, and the controversy helped contribute to his re-election defeat in early 1812.
The “gerrymander” succeeded that year; though the Federalists won the governor’s mansion, they could not retake the state Senate. But the very next year, the Federalists won such an overwhelming election victory that they took the state Senate, including the infamous gerrymandered district. Supportive media outlets celebrated the downfall of the gerrymander, as you can see depicted in this cartoon to the right:
There was much more to Gerry’s life than gerrymandering. He helped organize resistance against the British before the Revolutionary War, and signed the Declaration of Independence. But as a strong supporter of civil liberties, he refused to sign the Constitution out of principle, because it initially didn’t include a Bill of Rights.
Later, after Gerry lost his re-election as governor, he tried to get a federal position because he needed money. The result was his nomination for vice president, as James Madison’s running mate, in 1812 — Madison won, and Gerry died in office from an illness two years later.
But Gerry’s name has been inextricably attached to gerrymandering ever since. Even his name is frequently mispronounced because of the term — gerrymander is typically pronounced with a “J” sound, like “jerry,” but Gerry’s name should be pronounced with a hard “G.”
 Christopher Ingraham, This is the best explanation of gerrymandering you will ever see, The Washington Post, March 1, 2015, https://www.washingtonpost.com/news/wonk/wp/2015/03/01/this-is-the-best-explanation-of-gerrymandering-you-will-ever-see/?postshare=3561486810112140&tid=ss_tw-bottom&utm_term=.3e6c7704089b.
 Andrew Prokop, Gerrymandering, explained, Vox, May 15, 2015, http://www.vox.com/cards/gerrymandering-explained/what-is-gerrymandering.