A redistricting plan proposed by Republican legislators in Wisconsin in 2011 was overturned by a lower court based in part on the magnitude of the efficiency gap, although this ruling was overturned in 2018 by the US Supreme Court in Gill v. Whitford. In oral arguments, Chief Justice John Roberts dismissed this metric as “sociological gobbledygook.” Roberts’ critique is unfair in substance because the efficiency gap is a mathematical formula, not nonsense. But it is not entirely wrong in spirit. Some mathematicians have argued that these metrics do not accurately reflect “common-sense understanding of political unfairness.”

How can we identify gerrymandered maps if not by sight? Numerical metrics such as the Polsby–Popper test attempt to measure the “compactness” of an electoral district (the ratio of its area to the square of its perimeter), while the efficiency gap calculates the number of “wasted” votes by computing the proportion of votes that are not used to elect a winner.

However, Texas, California, Missouri, North Carolina, and Virginia have recently approved unusual mid-decade redistricting plans in advance of the upcoming US House of Representatives election in November 2026, approving new maps designed to advantage either the Democratic or Republican party. Pending decisions by courts, legislatures, and voters may potentially extend these practices to other states such as Louisiana and Florida.

Except when courts intervene, as happened recently in Ohio and Utah, electoral district boundaries are normally redrawn once a decade, aiming to create legislative units that represent approximately the same number of people based on census data.

Democrats won’t be able to use reconciliation to enact the government-reform bill that House Democrats adopted in 2019, which among other things would create two weeks of early voting in all 50 states and put redistricting in the hands of nonpartisan, independent commissions.