History
The Impact of Gerrymandering on Democratic Representation
Quick fact
In the 2012 U.S. House elections, Republican candidates received about 49% of the national popular vote but won 54% of the seats, largely due to gerrymandering. The 'efficiency gap'—a measure of wasted votes—quantifies this distortion, and courts have used it to strike down extreme partisan gerrymanders.
Why this is interesting
You might believe that elections are decided by voters. But sometimes, the outcome is determined long before you cast your ballot—when the district lines are drawn.
Read the full explanation
Understanding The Impact of Gerrymandering on Democratic Representation
Think of a state as a pizza that must be cut into equal slices, each representing a district. But the people who cut the pizza get to decide the shape of each slice—and they can make them as wiggly as they want. This is redistricting: the redrawing of electoral boundaries, usually after a census, to ensure each district has roughly equal population. The problem is that the people drawing the lines often have a strong interest in staying in power, so they may draw lines to favor their own party. Two main techniques are 'cracking' and 'packing'. Cracking spreads a group's supporters thinly across many districts so they are a minority everywhere. Packing concentrates them into a few dense districts, wasting their votes in landslide wins. Both techniques create 'wasted votes'—votes that don't contribute to winning a seat—and that can flip which party wins control, even if they lose the statewide popular vote.
A deeper explanation
The core mechanism is the interplay between geography and the math of single-member districts. In a winner-take-all system, the party with slightly more voters wins the whole district. Gerrymandering exploits this by manipulating how voters are grouped. By 'cracking', you dilute opposition votes across districts; by 'packing', you stack them into a few districts, 'wasting' their surplus votes. The result is a partisan bias where one party can win more seats than its vote share. For example, a state with 50% Democratic voters and 50% Republican voters could be divided so Republicans win 70% of districts. Even when the overall vote is balanced, the map decides the outcome. This undermines democratic representation—the idea that government should reflect the will of the people—because some voters' choices carry less weight. While the Supreme Court has ruled racial gerrymandering unconstitutional, it has struggled to limit partisan gerrymandering, leaving a major challenge for democracy.