Gerrymandering, or the practice of manipulating electoral district boundaries for political gain, is a practice as old as America itself.
Where the lines are drawn affects both state and federal elections. For Congressional elections, states are divided into districts based on how many representatives they send to the House of Representatives. In these cases, partisan gerrymandering is often used to maximize the wins for their own party.
Gerrymandering often occurs to secure party control, favor incumbents, or dilute the voting power of certain demographic groups. There is a fine line between an appropriate amount of community representation and partisan favoritism. The ambiguity of the situation is exacerbated by the lack of standard measurements of fairness.
Visualization adapted from Stephen Nass's "How to steal an election"
Many of the resulting districts end up as strange, winding shapes that intentionally include or exclude populations for political gain.
As a result, even though Party A may win the popular vote, Party B may end up sending more representatives to congress. Whoever decides the lines decide whose vote is reflected. This can skew statewide representation, dilute minority votes, split communities.
The goal of gerrymandering is to maximize the partisan number of districts that will vote for your party. This partisan distribution requires balancing the risk of maintaining a comfortable lead with the need of minimizing vote wastage.
Place all of your opponent's supporters into a few foregone districts to maximize wasted votes
Distribute your own supporters evenly amongst the districts to ensure a comfortable majority
District lines are redrawn every 10 years to reflect the updated populations taken by the US Census.
In most states, district lines are drawn by the majority party of the state legislature and approved by governor. Even in states with alternative processes like Independent Commissions, there are seats specifically reserved for Democratic or Republican appointees, so there are no truly non-partisan redistricting committees.
Visualization adapted from All About Redistricting
To measure "fairness", numerous metrics have been proposed, including a measure of compactness (the ratio of perimeter to area, with the ideal being a perfect circle at 1) and more recently, the efficiency gap, which measures the number of both wasted vote and diluted votes.
The efficiency gap measures net wasted votes by both parties over the total votes. The metric is compared against the number of seats won to find any seat advantages attained by either party.
The Gill v. Whitford case heard by the Supreme Court in October 2017 offers an opportunity to set a precedent for a legal test of fairness.
Seat margin - (2 * vote margin)
Seat margin: share of seats won by the winning party minus 50%
Vote margin: share of votes won by the winning party minus 50%
For uncontested races, we assumed that the opponent would have won 25% of the votes, as both the Associated Press and the University of Chicago Law School utilized this 75-to-25 vote share assumption in their models.
Canada shifted to this model in 1960s, but in the US, politicians still name appointees to the district.
Algorithms group on compactness and grouping an equal distribution of voters, but have a difficult time factoring in shared communities of interest.
Allocates representatives proportionally to voting results across the state instead of the current Winner Take All model, which uniquely solves judicial meddling and natural geographic clustering.
While Proportional Representation would most fairly represent a state's interests, it also requires the most drastic changes to the current politican system. For now, the outcome of the Supreme Court's decision for Gill v. Whitford will potentially provide a precedent for states to test the fairness of districting as a single, universal standard.
“ If you can stack a legislature in this way, what incentive is there for a voter to exercise his vote? Whether it’s a Democratic district or a Republican district, the result is preordained in most of the districts[...] What becomes of the precious right to vote?”
— Ruth Bader Ginsburg