Unit 4.5 — Electoral Geography: Packing, Cracking, and Gerrymandering

Everything discussed so far in this unit — states, nations, boundaries, devolution, supranationalism — operates at the scale of whole countries or regions. Electoral geography zooms in to a much smaller and, for many students, much more immediately relevant scale: the shape of the lines that divide a single country into voting districts, and how drawing those lines differently, while keeping the same voters in the same places, can change which party wins an election without a single person's vote actually changing.

Redistricting and the basic problem

Most legislatures with geographically defined seats — the U.S. House of Representatives, state legislatures, city councils — divide their territory into districts, each electing one representative. Because population shifts over time, districts have to be redrawn periodically so that each one contains roughly the same number of people, a process called redistricting. In the United States, redistricting for congressional and state legislative seats generally happens once a decade, after each national census, since the census is what establishes each state's population and, by extension, how many congressional seats it gets and where the internal lines should fall to keep districts population-equal.

The requirement that districts be roughly equal in population was not always strictly enforced. Before the 1960s, many U.S. state legislative districts had gone decades without redrawing even as population shifted dramatically from rural to urban areas, producing wildly unequal districts — a problem geographers and political scientists call malapportionment. The Supreme Court's 1962 decision in Baker v. Carr opened the door for federal courts to review redistricting plans, and the follow-up cases through the mid-1960s established the "one person, one vote" principle: districts electing the same body must contain approximately equal population, so that a vote in one district carries roughly the same weight as a vote in any other district for the same office.

Gerrymandering: shaping districts for political advantage

Equal population alone does not prevent district lines from being manipulated. Gerrymandering is the deliberate drawing of electoral district boundaries to give an advantage to a particular political party, incumbent, or group, rather than to reflect compact, sensible, or communally coherent geography. The term dates to 1812, when Massachusetts Governor Elbridge Gerry signed into law a state senate district so oddly shaped — twisting to concentrate his political opponents' voters — that a newspaper cartoonist drew it with a head, wings, and claws added, dubbing the shape a "Gerry-mander" after the mythical salamander it was said to resemble. The word has described the practice ever since, in the United States and, more loosely, anywhere else district lines are drawn for partisan advantage.

Geographers and political scientists measure gerrymandering partly through a district's shape. A compact, contiguous district generally looks something like a circle, square, or reasonably regular polygon; a gerrymandered district often looks stretched, tentacled, or fragmented, because it has been drawn to snake through specific neighborhoods and pick up or avoid specific populations rather than to keep a community intact. One common quantitative measure is the Polsby-Popper score, which compares a district's area to the area of a circle with the same perimeter — a perfect circle scores 1.0, and increasingly irregular, elongated shapes score closer to 0 — giving analysts a numerical way to flag unusually distorted districts for further scrutiny, though shape alone doesn't prove partisan intent.

Packing and cracking: the two core techniques

Gerrymandering is usually accomplished through one of two complementary techniques, and AP Human Geography expects students to be able to distinguish them precisely.

• Packing concentrates as many of the opposing party's voters as possible into a small number of districts, so that the opposing party wins those districts by enormous, "wasted" margins — far more votes than needed to win — while the party doing the packing wins most of the remaining districts by safer, more efficient margins. A packed district might go 90% to one party; that party "wastes" a huge share of votes that produced no additional seats.
• Cracking does the opposite: it splits a concentrated population of opposing-party voters across several different districts, diluting their influence in each one so that they fall short of a majority everywhere, even though their combined numbers, kept together, might have been enough to win a district outright.

Packing and cracking are often used together across a single redistricting map: a party in control of the process packs some opposing voters into a few sacrifice districts while cracking the rest across many others, maximizing the number of total seats it wins for a given share of the overall vote. This is why gerrymandering is such a powerful tool: it can produce a legislative majority for a party even in an election where that party receives fewer total votes statewide than its opponent, a pattern political scientists sometimes measure using the "efficiency gap," which compares each party's total wasted votes (from both packing and cracking) across all districts in a state.

Race, representation, and the courts

Redistricting in the United States intersects directly with civil rights law. The Voting Rights Act of 1965, passed to dismantle discriminatory voting practices that had long suppressed Black political participation, has been interpreted by courts to sometimes require the creation of majority-minority districts — districts deliberately drawn so that a racial or ethnic minority group makes up a majority of the district's voters, intended to give that community a realistic chance of electing a candidate of its choice where it could not have done so if its voters were dispersed (cracked) across several majority-white districts instead. But drawing districts primarily by race raises its own constitutional questions: in Shaw v. Reno (1993), the Supreme Court ruled that a district's shape could be so extreme, and so clearly driven by race as the predominant factor, that it violated the Constitution's equal protection guarantee, requiring courts ever since to weigh the goal of minority representation against limits on how far race alone can drive a district's shape.

Who draws the lines

How much power any single party has to gerrymander depends heavily on who controls the redistricting process, and this varies by state and country. In most U.S. states, the state legislature draws congressional and state legislative district lines itself, meaning whichever party controls the legislature at the time of redistricting has substantial power to shape district boundaries in its own favor. A smaller but growing number of states have shifted redistricting authority to independent or bipartisan commissions specifically to reduce this incentive — California and Arizona are commonly cited examples of states using independent citizen commissions rather than the legislature itself. Many other democracies avoid the issue differently, using proportional representation systems where seats are allocated according to a party's overall vote share rather than through geographically defined single-member districts at all, largely eliminating the incentive to gerrymander in the first place.

Why this matters for the exam

Exam questions on this topic frequently present a simplified map — a grid of colored squares representing voters of two parties — and ask you to identify whether a proposed district plan represents packing, cracking, or neither, and to explain the resulting seat outcome compared to the overall vote share. Practice reading these grid-style prompts carefully: the number of total voters for each party usually stays the same across every version of the map, and the entire question is about how the district lines redistribute those same voters. Also be ready to connect packing and cracking to the compactness and equal-population principles discussed above, since a strong free-response answer often has to explain not just what happened to the district shapes, but why the resulting distortion runs against the "one person, one vote" fairness principle courts have tried to enforce since the 1960s.