Redistribution is the process, used in many Commonwealth countries, by which electoral districts are added, removed, or otherwise changed. Redistribution is a form of boundary delimitation that changes electoral district boundaries, usually in response to periodic census results. Redistribution is required by law or constitution at least every decade in most representative democracy systems that use first-past-the-post or similar electoral systems to prevent geographic malapportionment. The act of manipulation of electoral districts to favour a candidate or party is called gerrymandering.
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Australia
In Australia, redistributions are carried out by independent and non-partisan commissioners in the Commonwealth, and in each state or territory. The various electoral acts require the population of each seat to be equal, within certain strictly limited variations. The longest period between two redistributions can be no greater than seven years. Many other triggers can force redistribution before the chronological limit is reached. The redistribution is drafted by civil servants.
Canada
In Canada, the constitution mandates that redistribution occur "on the completion of each decennial census." District boundaries are based on electoral quotients, with some exceptions. When the census indicates that a population change has occurred, an independent boundary commission issues a report of recommended changes. Changes are only made if passed into law—by Parliament for national redistribution, by the provincial legislature for provincial redistribution.
India
India has an established process to redistribute its legislative districts. Redistributions are approved by political appointees to the Boundary Commission of India.
Ireland
Elections to Dáil Éireann and to councils and local authorities are by single transferable vote (STV), using geographic constituencies which return three or more representatives. The number of representatives for each district is proportional to population. Boundary revisions may involve changing the number of constituencies, reapportioning the number of representatives returned from them, or adjusting the constituencies' borders. For example, the Electoral (Amendment) Act of 2005 replaced the five-seat Meath constituency with two three-seat constituencies, Meath East and Meath West, both of which also acquired territory previously in other constituencies.
Redistribution is done by the Oireachtas, acting on the advice of the Constituency Commission which is an independent body established by the 1997 Electoral Act. Redistribution prior to 1977 was done without independent input and subject to the partisan concerns of the government of the day.
Japan
Japan does not have an established process to redistribute its legislative districts. The frequency of redistributions is irregular and not triggered a particular event. Redistributions are approved by the national legislature.
New Zealand
New Zealand has a fixed process to determine how its legislative districts are redistributed. Redistribution in New Zealand happens every five years following the census.
Philippines
In the Philippines, redistricting is carried out by Congress after every decennial census is published. However, Congress has never passed a general redistricting act, and instead redistricts provinces or cities piecemeal, or creates new provinces or cities with legislative districts. The last general redistricting law was via the ordinance in the 1987 constitution, which was based from the 1980 census. The creation of a new province or city needs the approval of the public via a plebiscite, while piecemeal redistricting does not need a plebiscite.
United Kingdom
In the United Kingdom, there are four Boundary Commissions (one each for England, Scotland, Wales, and Northern Ireland) responsible for reviewing the boundaries of Parliamentary constituencies. Members of Boundary Commissions are political appointees.
United States
In the United States, redistribution occurs after each decennial census. Most states' legislative district redistributions are approved by the state legislature. Supreme Court rulings (such as the one man, one vote principle) require that legislative districts have roughly equal populations.