Redistricting (sometimes called districting, line-drawing or mapmaking) is the process of carving up a jurisdiction into districts from which officials are elected. This includes dividing states into legislative districts as well as the U.S. House of Representatives.
Members of city councils, county commissions, state boards, and even the judiciary may also be elected from geographic regions. When that is the case, these localities also need to be redistricted from time to time.
Redistricting is done to ensure the principle of “one person, one vote”: that voting power and representation in our legislative chambers is distributed equally, based on population. Every 10 years, after decennial census data is released, states are required to redraw the lines to meet this equal population goal. Mid-decade redistricting may occur in some circumstances. Some states can opt to redistrict mid-decade, and a state will have to redistrict if a court orders new maps to be drawn.
Generally, the task of redistricting falls to state legislatures. Even in states where a commission has been handed redistricting responsibility, the process still includes some role for the legislature in most states.