4.6 Internal Boundaries

Countries divide their territory into internal units like states, provinces, counties, cities and school districts. These boundaries decide who pays which taxes, which schools children attend and who represents whom. Some internal boundaries are drawn to manage diversity: Nigeria has grown from three regions at independence to 36 states, partly to balance its ethnic groups, and India redrew many state lines along language lines in the 1950s.

The U.S. House of Representatives has 435 seats. After each 10-year census, the seats are reapportioned, or shared out, among the states by population (topic 1.3). Each state then redraws its district lines, which is called redistricting.

Districts must have nearly equal populations, a rule known as “one person, one vote,” which the Supreme Court set out in the 1960s. Under the Voting Rights Act of 1965, courts have struck down maps that weakened the voting power of racial or language minorities, though how far that protection reaches has been argued in recent Supreme Court cases. In most states the legislature draws the lines, while some states, including Arizona, Colorado, Michigan and Washington, use independent or bipartisan commissions. Redistricting usually happens once a decade, but some states have redrawn their maps mid-decade, as several states led by each major party did in 2025.

Gerrymandering is drawing district lines to give an advantage to one political party or group. The name comes from Massachusetts governor Elbridge Gerry, who in 1812 signed a map that included a district a newspaper said looked like a salamander.

There are two main techniques. Packing crowds the other side's voters into a few districts, so they win those by huge margins and waste votes. Cracking splits the other side's voters across many districts, so they fall short of a majority in each. Both major U.S. parties have used gerrymandering when they controlled the process.

The courts have set limits. In Shaw v. Reno (1993), the Supreme Court allowed challenges to districts drawn mainly on the basis of race. In Rucho v. Common Cause (2019), it ruled that federal courts can't decide claims of partisan gerrymandering, leaving the issue to states and Congress.

• Local: city council and school board districts decide which neighborhoods get a representative who reflects their interests.
• State: maps for the state legislature can lock in one party's control even when statewide votes are close.
• National: the combined district maps of all the states help decide which party controls the U.S. House.
• Other democracies, like the United Kingdom and Canada, use independent commissions to draw boundaries.