Redistricting is the process of redrawing electoral district lines to adjust for population changes. The goal is to come up with districts that have as equal population as possible, while also achieving other goals that the government has identified.
After receiving new Census figures, all jurisdictions that use districts to elect representatives must make sure that their district populations are still equal. That means state-level districts, like State Assembly, as well as local districts, like city councils, school boards, and special districts.
The information in this website focuses on redistricting for state-level districts: US House of Representatives, California Senate, California Assembly, and California Board of Equalization districts. While much of the information will be the same for your local-level districts, like your city council or school board, some of it will be different. If you want to know what rules or criteria govern redistricting for your local-level district, you should contact that jurisdiction for information.
In the 1960s, the US Supreme Court heard a case alleging that decades of maintaining the same districts had led to inequalities in district populations. That is, some districts had very large populations while others had very small populations. The Supreme Court found that this population inequality (also called malapportionment) was a violation of the US Constitution’s guarantee to equal protection. This is because the votes of people living in very populous districts were ‘worth less’ than the votes of people living in less populated districts. As a result, in order to comply with the Constitution, districts must contain about the same number of people so that votes are “worth” about the same amount. This is sometimes called the “one person, one vote” requirement.
Every ten years, the Census performs a count of all people living in the United States. The Census tells us where populations are located and how they have changed. The population can change a great deal in ten years due to people moving, people dying, people being born, etc. After the Census data is released, we can see how district populations have changed. We often see that districts that were equal ten years before, have become malapportioned due to population changes. That is, some districts have too many people while others have too few people.
Jurisdictions that use districts for elections must redistrict in order to make the populations in districts equal again and ensure they are complying with “one person, one vote” requirements.