Redistricting

What is Redistricting?

The Enumeration Clause is found in Article I, Section 2, Clause 3 of the U.S. Constitution. It governs how representatives in the House of Representatives are apportioned, stating no more than one representative per 30,000 people, but each state must have at least one. This means a state may gain seats if its population grows or lose seats if it decreases, relative to populations in other states.

Redistricting is the process of redrawing the boundaries of congressional and state legislative districts so that each electoral district is balanced and has fair representation. Because people move, cities grow, and populations shift, updating boundary lines is necessary to ensure that each elected official represents a similar number of residents.

The U.S. Census is conducted every 10 years, determining both congressional apportionment and federal funding allocations. The Enumeration Clause remains central to U.S. political representation and federal governance.

How Does Redistricting Work?

Congressional boundary lines have developed from simple, county-based outlines into highly structured districts shaped by population data, legal standards, and the authority responsible for drawing them.

1. 1
   The census sets the stageEvery ten years, the U.S. Census counts the population. States use this data to see which areas gained or lost people.
2. 2
   States receive updated district numbersSome states gain or lose seats in the U.S. House based on population changes in a process called reapportionment.
3. 3
   Map-drawing beginsDepending on the state, new district maps may be drawn by the state legislature, an independent or bipartisan commission, or a hybrid system.
4. 4
   Draft maps are created and debatedMapmakers use population data, demographic information, and legal requirements (such as the Voting Rights Act) to draw proposed district lines. Public hearings often occur during this stage.
5. 5
   Approval of the final mapThe legislature or commission votes on the map. In some states, the governor can approve or veto it.
6. 6
   Legal challenges may followIf groups believe the map is unfair or discriminatory, they can sue. Courts may require changes or even redraw the map themselves.
7. 7
   New districts take effectOnce finalized, the new boundaries are used in the next election cycle.

What is Mid-Decade Redistricting?

Instead of waiting for the next census cycle, some states opt to redraw voting district boundaries sooner. Mid-decade redistricting is often considered controversial because it can significantly shift political power.

The steps for mid-decade redistricting look similar to regular redistricting, but the trigger is different. A reason may emerge because a court rules that the existing map violates the law, a new political majority wants to redraw the lines, population changes create representation concerns, or a state's constitution or laws allow redrawing at any time. Mapmakers then draft new boundaries using existing census data and must still follow legal rules such as equal population and protections for minority voters.

Possible legal challenges are common: mid-decade redistricting often ends up in court because opponents argue it is unfair, unnecessary, or politically motivated.

States That Have Completed Mid-Decade Redistricting

States with Activity or Steps Considered

Source: NCSL's Changing the Maps: Tracking Mid-Decade Redistricting - last updated April 2026

Who Draws the Redistricting Maps?

In the early years of the republic, state legislatures handled the task almost entirely on their own, often relying on broad geographic units because detailed maps and demographic tools were limited. Over the 20th century, the decennial census became the foundation for assigning House seats, which required states to redraw their districts every ten years.

In recent decades, some states have transferred redistricting power from legislatures to independent or bipartisan commissions, aiming to reduce partisan influence. Other states have kept the authority in the hands of lawmakers, maintaining a system where political majorities can shape district boundaries.

What Factors are Considered During the Redistricting Process?

Redistricting takes many different considerations into account. Some are legal requirements, while others reflect policy choices or political priorities. The balance among them can vary widely depending on whether a state legislature or an independent commission is in charge.

• Equal PopulationDistricts must contain roughly the same number of people so each resident's vote carries similar weight, the "one person, one vote" principle.
• Voting Rights Act ComplianceDistrict lines must not weaken the voting power of racial or language-minority groups, including avoiding dilution of minority communities.
• ContiguityEach district must be one connected shape, it cannot be made of scattered, unconnected fragments.
• CompactnessDistricts should not sprawl in odd, stretched-out shapes without a clear geographic or community reason.
• Communities of InterestMapmakers try to keep together groups of people who share social, cultural, economic, or geographic ties.
• Existing Political BoundariesMany states try to avoid splitting counties, cities, or towns unless necessary, since these areas often function as unified communities.
• Partisan ConsiderationsIn states where legislatures control redistricting, political advantage can influence how lines are drawn, including protecting incumbents.
• Public InputMany states require hearings or allow citizens to submit map proposals, adding community perspectives to the process.

What is Gerrymandering?

Gerrymandering is the practice of manipulating electoral district boundaries to give an unfair advantage to a particular political group or incumbent. Instead of reflecting natural communities or ensuring fair representation, map-drawers reshape districts in ways that dilute some voters' influence while amplifying others'. Critics argue that gerrymandering undermines democratic accountability and distorts election outcomes, while supporters sometimes claim it is an inevitable part of political map-drawing.

Packing and cracking are two of the most common techniques. In packing, map-drawers concentrate as many targeted voters as possible into a single district, giving them overwhelming majorities there while reducing their influence everywhere else. In cracking, the opposite happens: the group is split across multiple districts so that they form only a small minority in each one, making it harder for them to elect their preferred candidates. Together, these tactics reshape political maps in ways that can distort representation and tilt outcomes toward the party controlling the redistricting process.

How is Census Data Used During Redistricting?

Thirty states specifically mandate the use of federal census data when drawing either state legislative districts, congressional districts, or both. In addition, Oregon's case law also requires census data for its state legislative redistricting.

Twelve other states do not clearly state what data must be used. Even so, their statutes either imply reliance on the decennial census or, in practice, default to using census figures. Eight states permit the use of alternative data sources, allowing the legislature to choose something other than decennial census data.

Source: NCSL's Redistricting and Use of Census Data - last updated October 2025

How do States Change the Way Redistricting is Done?

States use a range of legislative strategies to reshape how redistricting works, often aiming to change who controls the process or what rules guide it. Lawmakers may pass statutes that redefine the criteria map-drawers must follow, shift authority to independent commissions, or adjust procedures for public input. These legislative changes can significantly influence how districts are drawn and how representative the final maps are.

Source: Ballotpedia's Election Administration Legislation Tracker - last updated May 2026

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