Civic primer

How districting works

Every ten years the country counts itself and redraws its political maps. This is a plain-language reference to how that works — the census, how U.S. House seats get divided among the states, how each state redraws its own district lines, who holds the pen, and what "gerrymandering" actually means. Neutral by design: we define the mechanisms and link the sources; we don't accuse.

On this page

What districting is
The census: the 10-year clock
Apportionment (dividing the seats)
Redistricting (drawing the lines)
Who draws the maps
The rules a map must follow
Majority-minority districts
Gerrymandering, defined
How to see it yourself
Sources & further reading

In one sentence After each decade's census, the 435 U.S. House seats are re-divided among the states by population (apportionment), and then every state redraws its own district maps to match (redistricting) — and because whoever draws the lines can shape who wins, both steps are closely watched.

This is the deeper dive behind the civics primer's district section. For the quick version — and the crucial "whose Senate?" distinction between the four overlapping districts every address sits in — see Learn §4: Districts, apportionment & redistricting.

What districting is

A district is a geographic area that elects one representative. To vote for a member of the U.S. House, a state legislator, or many local offices, you have to be sorted into a district — and someone has to draw the boundary that decides which district your address falls in. Districting is that whole process: deciding how many districts there are, and where the lines go.

Two separate steps make it up, and they're constantly confused: apportionment decides how many seats each state gets, and redistricting decides where the lines are drawn inside a state. Both are triggered by the same event — the census — on the same ten-year clock.

The U.S. Senate has no districts at all: every state elects two senators statewide, regardless of population, so nothing about the census changes the Senate. Districting is a House and state-legislative (and local) matter.

The census: the 10-year clock

The Constitution requires an "actual Enumeration" of the population every ten years — the decennial census, run by the U.S. Census Bureau in years ending in zero (2020, 2030, …). It's the count that starts everything: the population totals it produces are the numbers used to apportion House seats and to redraw districts.

For map-drawing specifically, the Bureau delivers a special tabulation called the P.L. 94-171 redistricting data — population counts down to the census-block level, broken out by race and voting age — to every state. That block-level data is the raw material every map-drawer starts from.

Apportionment (dividing the seats)

Apportionment is the first thing to happen after the count: the 435 seats in the U.S. House are re-divided among the 50 states in proportion to their populations. Fast-growing states gain seats; slower-growing ones lose them. Every state is guaranteed at least one seat no matter how small.

The 435 total has been fixed by law since the Permanent Apportionment Act of 1929; the seats are distributed using a formula called the method of equal proportions, which assigns each seat to the state with the highest "priority value" until all 435 are placed. The result also sets each state's number of Electoral College votes (House seats + 2 senators) — the link to how presidents are chosen (see The Electoral College).

Apportionment is purely federal and purely arithmetic — no lines are drawn, just seat counts assigned. The Senate is untouched (always two per state). It's the step that decides, for example, that Texas gains seats while New York loses one.

Redistricting (drawing the lines)

Once a state knows its seat count, it must redistrict — actually draw the boundaries. And a state doesn't draw one map, it draws several, each on its own:

Congressional — the state's U.S. House districts, one per apportioned seat. (A state with a single seat is "at-large" and draws none.)
State Senate — the districts for the state's own upper chamber.
State House / Assembly — the districts for the state's own lower chamber.

Those are three different maps with three different sets of lines, and — this is the key point — a state can use a different process for each one. Local governments (county boards, city councils, school boards) redraw their own districts too.

Almost all of these seats are single-member: one district, one winner, whoever gets the most votes. Because the winner is decided district-by-district, where the lines go can change which side wins a chamber even when no one's vote changes.

Who draws the maps

There's no single national answer to "who holds the pen" — it's set state by state, and can differ for the congressional map versus the state-legislative maps. The main models:

Who draws	How it works
The legislature	The most common model: the state legislature passes the maps as ordinary bills, usually subject to the governor's veto. The party in control of the statehouse controls the pen.
Independent commission	An outside body (members chosen to be independent of the legislature) draws the maps to take the pen out of legislators' hands. Arizona, California, Michigan and others use these for congressional and/or legislative maps.
Politician / bipartisan commission	A commission made up of officials or party appointees (e.g. a fixed split of both parties, sometimes with a tie-breaking member) rather than independent citizens.
Advisory / backup & the courts	Some states use an advisory commission, or a backup commission that acts only if the legislature deadlocks. When a map is struck down or no map passes in time, a court can draw or order one.

The National Conference of State Legislatures keeps the current, state-by-state breakdown of who draws which map.

The rules a map must follow

Map-drawers aren't free to draw anything. Districts have to satisfy a set of legal and traditional criteria — some required by the Constitution or federal law, some by each state's own rules:

Equal population. Under the "one person, one vote" principle, districts within a plan must hold nearly equal numbers of people — very tight for congressional maps, with a small allowance for state-legislative ones.
The Voting Rights Act. Federal law (Section 2 of the VRA) bars maps that dilute the voting strength of racial or language-minority groups.
Contiguity. A district must be one connected piece — you can travel across it without leaving it.
Compactness. Many states ask that districts be reasonably compact rather than sprawling or oddly shaped.
Communities & boundaries. Many states require respecting existing lines — counties, cities, and "communities of interest" — where possible.

Majority-minority districts

A majority-minority district is one in which a racial or ethnic minority group makes up a majority of the population (or of eligible voters). These districts exist largely because of the Voting Rights Act: where a minority community is large and geographically compact enough, and voting is racially polarized, Section 2 can require drawing a district in which that community has the opportunity to elect a candidate of its choice.

This is one of the genuinely hard balances in map-drawing: the VRA can require that race be considered to avoid diluting minority votes, while the Constitution's Equal Protection Clause limits maps in which race was the predominant factor. Where that line sits has been litigated repeatedly — CivicGate's posture is to describe the legal test, not to score any given map.

Gerrymandering, defined

Gerrymandering is drawing district lines to favor one group over another — a party, an incumbent, or a faction — rather than to reflect neutral criteria. The word dates to an 1812 Massachusetts map whose district was said to resemble a salamander. It works through two basic moves:

Packing — concentrating a group's voters into as few districts as possible, so they win those by huge margins but their strength is "wasted" and doesn't spread to other seats.
Cracking — splitting a group's voters across many districts so they fall short of a majority in each one, winning none.

Both moves aim at the same thing: converting a given share of voters into more or fewer seats than that share would otherwise produce. Gerrymandering can be partisan (for a party) or racial (targeting a racial group — which can violate the Voting Rights Act).

CivicGate's posture here is deliberately neutral: an oddly shaped or lopsided district is a fact to describe, not a verdict to pronounce. Shapes can be irregular for innocent reasons (rivers, county lines, where people actually live), and courts — not a website — decide whether a specific map crossed a legal line. We define the mechanism and link the sources; the judgment is yours.

How to see it yourself

Districting output is public. The maps on CivicGate's Find your reps page and the district pages are today's federal congressional districts — the current lines from the most recent redistricting cycle (state-legislative districts are a planned addition). To go to the primary record:

Find your reps — enter an address to see which congressional district it sits in and who represents it.
The Census Redistricting Data Office — the block-level population data every map is built from.
All About Redistricting (Loyola Law School) — a neutral, state-by-state guide to each cycle's rules and litigation.

Sources & further reading

This primer summarizes official and authoritative, non-partisan sources:

CivicGate is a neutral reference. This page explains how districting works; the Find your reps page shows the current maps, and the broader civics primer puts districts in context with Congress, elections, and money.