Cracking and packing explained
Gerrymandering is the drawing of electoral district boundaries to favor one party or group. Its two core tactics are cracking and packing. Cracking splits a bloc of like-minded voters across many districts so they fall short of a majority in each and elect no one. Packing does the opposite, concentrating opposing voters into a few districts they win overwhelmingly, wasting their surplus votes and leaving surrounding districts safely favorable.
Because both tactics manipulate where votes are wasted, the same statewide vote totals can translate into very different seat counts depending only on how the lines are drawn.
Measuring and recognizing gerrymanders
Gerrymandered districts often have contorted, sprawling shapes, which is where the term originated: an 1812 Massachusetts district under Governor Elbridge Gerry was likened to a salamander. Shape alone is not proof, so analysts use quantitative tests.
Compactness scores compare a district's area to its perimeter or to a circle, while the efficiency gap counts each party's wasted votes (those cast for losers plus surplus votes beyond a majority) and flags large imbalances. Ensemble methods now generate thousands of neutral random maps to see whether an enacted map is a statistical outlier.