Malapportionment

A district exists to translate a body of people into a legislative seat. When districts are drawn or left unchanged for long enough that populations shift, the translation goes wrong: a rural seat of 40,000 residents elects one member, and so does an urban seat of 200,000. The rural voter's share of that seat is five times larger. That ratio — not any question of who lives there or how they vote — is the definition of malapportionment.

Malapportionment happens in two distinct ways, and the distinction matters legally. Passive malapportionment is drift: boundaries fixed at one census become increasingly skewed as people move. Active malapportionment is design: someone draws lines knowing the resulting populations are unequal, typically to advantage the majority that controls the redistricting process. The outcomes can look identical on a map. Intent is what differs, and intent is what courts have to establish.

The United States produced the canonical rulings. Before Wesberry v. Sanders (1964) and Reynolds v. Sims (1964), congressional and state legislative districts varied enormously in population within the same state. The Supreme Court's "one person, one vote" standard required equality "as nearly as practicable" for congressional districts and substantial equality for state legislatures. The United Kingdom ran a version of the same problem before independent boundary commissions were given regular review cycles: by the 1990s some English constituencies had electorates twice the size of others. Japan's Supreme Court repeatedly found its own apportionment unconstitutional into the 2010s, with rural districts retaining seats their falling populations no longer justified.

The remedy is periodic redistricting tied to census data, but the remedy introduces its own choices. Perfect population equality across every district is arithmetically achievable and politically contentious — it can require splitting cities, counties or communities of interest to hit a number. Most systems therefore accept a small tolerance band, and the width of that band is itself a legislative decision. A tight band limits drift and leaves less room to manoeuvre; a loose one creates opportunity. Who draws the line — legislature, commission or court — shapes how that opportunity is used.

Malapportionment is not gerrymandering, though the two are often confused. Gerrymandering is about shape and composition; malapportionment is about size. A district can be perfectly round and still contain a population a fraction the size of its neighbour. Separating the two concepts is the first step to diagnosing which problem a particular map actually has.