Let’s imagine a fictional place: the great state of Gratewood.
Gratewood has two political parties, the Gold Party and the Purple Party. It has exactly 1000 residents, and those residents are represented by 10 representatives in the legislature.
The fortunes of the two political parties change from year to year, but in this election cycle, the people are about 60% Gold Party and about 40% Purple Party.
The state is divided into ten districts of 100 citizens, and each district chooses a representative.
If the districts are drawn without regard to composition, and the distribution of party members is roughly random, then every district will have about 60 Gold Party voters and 40 Purple Party voters. The Gold Party will win every single district, and the Purple Party that makes up 40% of the population will have no representation.
The Purple Party doesn’t like this situation. They are drawing the maps this year, and they want to insure that their minority controls the legislature. How can they manage this?
The goal is to give as many districts as possible a majority of Purple Party members. There are 400 Purple Party members in the state. If they draw the districts to their advantage, they could have a 57/43 split in favor of the Purple Party in 7 districts, with the remaining 3 districts packed with the Gold Party people. Even though the Purple Party is a minority of the population, they can maintain a large majority advantage in the legislature.
And in this (highly simplified) scenario, even if the Gold Party grows in numbers, the Purple Party can hold on to control of the legislature until the Gold Party gets about 70% advantage at the polls… as long as the Purple Party legislators are allowed to draw the district maps.
That’s gerrymandering, and it’s called that because the resulting districts often look like weird salamanders crawling across the map as legislators try to cram as many of their opponents into as few districts as possible.