How Redistricting Works

Redistricting is the process of redrawing voting district lines to reflect population changes. It’s an important part of our democracy.

Redistricting happens every 10 years, after each U.S. Census. This means that after the 2020 census is completed, new lines will be drawn for several types of voting districts:

When you vote, it’s for representatives within your assigned districts—that’s why they’re sometimes called voting districts. But your district matters just as much beyond Election Day: When you want to speak up about an issue or ask for help with a government service, you’ll go to your elected representatives within your assigned districts.

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Why redistricting happens

The process is complicated, but you don’t have to be a politician or a policy wonk to understand the basics. Here’s what you need to know.

In the U.S., representation is based on population: the more people in an area, the more representatives it gets (except in the U.S. Senate, where each state gets two senators, no matter what). As populations change and move around, we need to update the size and shape of districts, so each lawmaker continues to represent a fair portion of the population.

In 1964, the Supreme Court ruled that the Equal Protection Clause of the 14th Amendment of the Constitution requires that voting districts be equal in population. Chief Justice Warren wrote in the majority opinion that “legislators represent people, not trees or acres” and “legislators are elected by voters, not farms or cities or economic interests.” Because of this ruling, voting districts are now drawn to be equal in population. But that alone doesn’t make them fair—because how those new lines get decided still isn’t equal.

The redistricting process

Article 1, Section 4 of the Constitution gives the states primary authority to regulate federal elections, including congressional redistricting. However, it also says that Congress is the ultimate authority and may supersede state laws. Congress has exercised this authority—for example, to require single-member districts (instead of multi-member districts) and to enhance racial and ethnic minority groups’ representation—but it has never mandated specific procedures for redistricting, despite many bills that have been introduced.

Congressional redistricting


Congressional redistricting starts with reapportionment. Because the U.S. House of Representatives always has a total of 435 seats, the country must always be divided into 435 congressional districts. But some states are growing, while others aren’t. Reapportionment is the process of adjusting how many of those 435 seats each state should get, depending on how the country’s population has changed since the last census. States gaining population are most likely to gain House seats while states with stable or declining populations are likely to lose seats.

That’s why Pennsylvania lost one House seat after the last census, and we’re projected to lose one or two more in 2020.

After each state learns its new number of districts, the lines need to be redrawn so that each district has roughly the same number of people. All states have to be redistricted to account for population shifts, but states that have gained or lost seats—like Pennsylvania—tend to have the most changes. This is one of the reasons we’re such a target for gerrymandering.

Congressional redistricting in Pennsylvania is done through the regular legislative process. A bill defining district boundaries is passed by both the PA House and Senate and signed by the governor. The problem is, Pennsylvania law doesn’t say how congressional districts should be redrawn or what criteria should be used to ensure new district boundaries are fair. If the legislature and governor belong to the same party, that party, can end up with exclusive control over the result.

State legislative redistricting

PA House and Senate districts are called state legislative districts. Article II, Section 17, of the Pennsylvania Constitution mandates that these districts be drawn by a five-member commission. Four of these are the majority and minority leaders of the PA House and Senate. These four pick a fifth person to be chair. If they can’tagree, the majority of the PA Supreme Court appoints a chair.

This commission has exclusive authority to draw the maps. Article II, Section 16 of the Pennsylvania Constitution requires these districts “be composed of compact and contiguous territory as nearly equal in population as practicable” and to avoid dividing a “county, city, incorporated town, borough, township or ward” unless absolutely necessary.

The Legislature does not vote on the commission’s plans, and the governor has no power to sign or veto them. This gives party leaders enormous power over the mapping process. In effect, it also lets incumbents draw their own districts—a clear conflict of interest from the start.

It’s time for change

Currently, the only way to fight for fair districts is with lawsuits. The 2010–11 redistricting process resulted in multiple lawsuits that cost Pennsylvanians millions of dollars in legal fees and caused confusion among voters and election officials waiting for appeals to be decided.

Fair Districts PA advocates amending the PA Constitution to establish an independent citizens commission with clear rules about public input, use of data and how the maps should be drawn.

Learn about our plan for reform