Redistribution (re-districting in the United States and in the Philippines) is the process by which electoral districts are added, removed, or otherwise changed.
[citation needed] The act of manipulation of electoral districts to favour a candidate or party is called gerrymandering.
In Canada, the Constitution mandates that redistribution in the federal House of Commons occur "on the completion of each decennial census.
The Constitution of Ireland states that general elections to the Dáil (lower house) must use the single transferable vote (STV), that each Dáil constituency must return at least three members (TDs), that boundaries must be revised at least every twelve years, and that the ratio of TDs to inhabitants (not voters or citizens) be between 20,000 and 30,000 on average and "so far as it is practicable" equal between constituencies.
[5] In constituencies for the next general election, the 2016 population per TD averages 29,762, varying from 28,199 in Dublin North-West to 31,270 in Dún Laoghaire.
[5] The terms of reference of the Commission have set five seats as the maximum and discourage constituencies crossing county boundaries.
Another proposal, rejected simultaneously, would have established a constituency commission (ancillary to replacing STV with first-past-the-post voting).
There was a lacuna after the publication of the 2016 census results in which the Electoral (Amendment) (Dáil Constituencies) Act 2013 was in force but its 158 seats breached the 30,000 population average; jurists wondered whether the courts would have permitted a general election in the interim before the Electoral (Amendment) (Dáil Constituencies) Act 2017 resolved the issue.
[13] In Mexico, an independent administrative body, called the Instituto Nacional Electoral, redraws congressional districts according to an objective scoring function and optimization algorithm.
Supreme Court rulings (such as the one man, one vote principle) require that legislative districts have roughly equal populations.