What is Gerry?
Gerry is a redistricting simulator that demonstrates how drawing district boundaries can determine election outcomes independently of how people vote. Players partition a procedural hex-tile map of voters into districts and immediately see how their choices affect six fairness metrics.
Redistricting Mechanics
The map generates voters affiliated with three political parties, distributed across population centers with realistic urban-suburban-rural gradients. Players paint hexes to assign them to districts. Each district elects one representative by plurality vote. Real-time feedback shows vote shares, seat counts, and all six fairness metrics as boundaries change.
Fairness Metrics
Six metrics evaluate every map: the efficiency gap (wasted votes as a fraction of total), partisan symmetry (whether both parties are treated equally), competitive district count (margins under 10%), compactness via the Polsby-Popper ratio, contiguity (no isolated fragments), and majority-minority district count. No single metric captures fairness completely — the simulation shows how they can conflict.
Algorithms
Two automated modes contrast deliberate gerrymandering with fairness optimization. Pack-and-crack concentrates opposition voters into a few districts while spreading the rest thin. The fair draw algorithm uses simulated annealing to optimize compactness and partisan symmetry simultaneously. Monte Carlo elections stress-test any map by running thousands of elections with turnout noise.
Voting Rights Context
In the United States, the Voting Rights Act of 1965 requires that redistricting not dilute the voting power of racial or ethnic minorities. This often means creating majority-minority districts where minority communities can elect their preferred candidates. Gerry models this constraint by tracking majority-minority district counts and requiring a minimum of two, illustrating the tension between compactness, proportionality, and representation.
Accessibility
Gerry supports keyboard navigation for all controls, high-contrast mode via the theme toggle, and ARIA labels on toolbar buttons and metric displays. District assignments are visible through both color and numerical labels. No flashing content or motion simulation hazards.
See also: Geon for particle physics, Shoals for options trading, Cyano for cellular metabolism.
Learning Outcomes
After using Gerry, students should be able to: explain how pack-and-crack strategies manufacture electoral majorities from minority vote shares; compute the efficiency gap for a given district map and interpret values above the 8% threshold; describe the trade-off between compactness and proportional representation; and evaluate why contiguity alone is insufficient to guarantee fair districts.
Prerequisites
No prerequisites beyond basic arithmetic. The simulator introduces all fairness metrics with visual feedback — no prior knowledge of electoral law or political science is needed.
References
N. Stephanopoulos and E. McGhee, "Partisan Gerrymandering and the Efficiency Gap" (2015). D. Polsby and R. Popper, "The Third Criterion: Compactness as a Procedural Safeguard Against Partisan Gerrymandering" (1991). Rucho v. Common Cause, 588 U.S. ___ (2019).