For teachers
Teach redistricting on a real map
Gerrymeandering is a free redistricting game. Students draw congressional districts on a real US state, then see the districts actually in use drawn over their own map. One state takes about ten minutes, so it fits inside a single class period with time to talk.
- FreeNo purchases
- No sign-upNo account or login
- Any browserChromebooks included
- All 50 statesReal Census maps
What students do
Each student, or each pair, gets a state and a side, and one goal: win as many seats for that side as they can. The map is built from Census geography, with 2024 presidential vote returns spread across it.
They split the state into districts. The game only accepts a map whose districts are contiguous and equal in population. When they submit, the 119th Congress’s actual districts draw over their map: the same state and the same voters under two plans. Their map is scored against the enacted one on seats won, Polsby-Popper compactness and the efficiency gap.
Every state can be played from either side, and both sides are scored the same way.
What it teaches
Redistricting is usually taught definitions first: packing, cracking, then the efficiency gap formula. Gerrymeandering runs that order in reverse.
On a real state, the only way to win extra seats is to pack the other side’s voters into a few districts they win by huge margins and crack the rest across districts they narrowly lose. Students do both before anyone names them. The efficiency gap then arrives as a number on their own results screen, from a map they drew, and compactness shows them the trade-off between winning seats and drawing tidy shapes.
- Packing
- Concentrating one side’s voters into a few districts so their extra votes are wasted.
- Cracking
- Spreading one side’s voters thinly across many districts so they fall short in each.
- Efficiency gap
- The difference between the two sides’ wasted votes, as a share of all votes cast. A wasted vote is any vote for a losing candidate, or any vote for a winner beyond the bare majority needed.
- Compactness
- How close a district’s shape is to a circle. The game uses the Polsby-Popper score: 4π × area ÷ perimeter².
- Population balance
- Every district must hold close to the same number of people. The game won’t accept a map that breaks this, or one with a district in pieces.
One class period, 50 minutes
No reading beforehand and no vocabulary up front.
- 5 minSet up. Put students in pairs. Give every pair the same state, ideally your own, and split the room so half play each side. Tell them only the goal: win as many seats as you can.
- 15 minDraw. Leave them alone. Pairs will argue, and that’s useful.
- 5 minSubmit. Each pair writes down three numbers: seats won, compactness and efficiency gap. Then they look at the enacted map over theirs.
- 10 minName it. Put two maps on the projector, one from each side. Point to a district that’s 80 percent one side and ask what it’s for: that’s packing. Find a city split four ways: that’s cracking. Then show the efficiency gap as the number they already wrote down.
- 10 minDiscuss. Use the questions below.
- 5 minExit ticket. One sentence: what would a rule have to say to stop what you just did?
The game has been tested with playtesters but not yet in a classroom, so treat this as a starting point rather than a proven plan.
Discussion questions
These work for a section of thirty or a lecture of three hundred.
- Is either map fair? Your map and the enacted one turned the same votes into different seat counts. What would “fair” have to mean before you could answer?
- Which number should a court care about? Your best-scoring map and your most compact map were probably different maps. In Rucho v. Common Cause (2019), the Supreme Court held that federal courts can’t decide partisan gerrymandering claims. If not courts, who enforces any of these numbers?
- What did you need to know? You drew a winning map using nothing but last year’s presidential vote. Real mapmakers have far better data. Should they be allowed to use it?
- Can you tell who drew it? Michigan’s map is drawn by an independent citizens commission; most states’ maps are drawn by legislators. Draw one of each. Can you tell which is which from the overlay alone?
What it leaves out
Worth saying to the class up front.
- The overlay is the 119th Congress map. Several states, including North Carolina, Ohio, California, Utah and Texas, adopted newer maps for 2026. In those states the overlay shows the previous plan, which makes a good discussion.
- Presidential votes stand in for every race. People don’t vote the same way all the way down the ballot. Real mapmakers model that; the game doesn’t.
- Most of the law is missing. Contiguity and equal population are enforced. There’s no Voting Rights Act requirement, no communities of interest and no protection for incumbents, so students solve a simpler problem than a real legislature does.
- It asks students to gerrymander. That’s deliberate. What keeps it nonpartisan is that every state can be played from either side and scored the same way, so the debrief is about what the geometry allows rather than which party to blame.
Before class
Play one state yourself first, ideally the one you plan to set. The browser version at gerrymeandering.subastra.dev is the one built for class: it runs in any browser, Chromebooks included, and needs no installs or student accounts. There are free iPhone and Android versions too.
For homework, the Daily mode gives every player in the world the same state and the same side each day, so the next morning’s comparisons are fair. Forty short levels on invented states build up gradually if students need a warm-up.
Used it in class?
Gerrymeandering is made by Subastra, a small studio in Chicago. If you try it with students, Subastra would like to hear what worked and especially what didn’t. Questions about the lesson or the data are welcome too.