This article needs additional citations for verification. (July 2012)
Redistribution (redistricting in the United States and in the Philippines) is the process 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.
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.
In Canada, the Constitution mandates that redistribution in the federal House of Commons occur "on the completion of each decennial census." The number of seats amongst the ten provinces is set by several related constitutional provisions. District boundaries within provinces are based on electoral quotients for that province. 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 the federal Parliament.
Similar processes are followed in each province, under provincial law.
India has an established process to redistribute its legislative districts. Redistributions are approved by political appointees to the Boundary Commission of India.
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. Electoral Acts are passed by the Oireachtas to revise boundaries in light of the most recent census. 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. Since 1977, an independent body (since 1997 a permanent Constituency Commission) recommends boundaries, which the Oireachtas usually accepts. The terms of reference of the Commission have set five seats as the maximum and discourage constituencies crossing county boundaries.[n 1] A separate Local Electoral Area Boundary Committee fulfils a similar function for local electoral area boundaries. A proposed Electoral Commission would replace both the Constituency Commission and the Local Electoral Area Boundary Committee.
Before 1977, boundary drawing was often partisan in favour of the government of the day. The Electoral (Amendment) Act 1959 was struck out in 1961 by the Supreme Court as being repugnant to the Constitution because of excessive malapportionment. The replacement Electoral (Amendment) Act 1961 relied on manipulating district size[n 2] The Supreme Court allowed the 1961 Act, ruling that the Oireachtas had wide latitude to decide what degree of divergence was "practicable" and what factors could be considered, but reserved the right to judicial review of proposed boundaries. A 1968 proposal rejected by referendum would have specified one-sixth as the maximum constituency divergence from the average population per TD. Another proposal, rejected simultaneously, would have established a constituency commission (ancillary to replacing STV with first-past-the-post voting). The Electoral (Amendment) Act 1974 attempted a manipulation similar to the 1961 act, but backfired when a larger than expected swing created a tipping point favouring the opposition in 1977. 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.
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.
In Mexico, an independent administrative body, called the Instituto Nacional Electoral, redraws congressional districts according to an objective scoring function and optimization algorithm. Although political parties can propose maps, the process is largely influences by redistricting algorithms.
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.
In the Philippines, redistricting is carried out by Congress after every quinquennial 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.
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.
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.
- Large counties may be split into multiple constituencies, and small counties paired in a single constituency, but combining part of one county with part or all of another causes controversy.
- Where the Fianna Fáil party of the then government had less than 50% support, four-seat constituencies were used, so that Fianna Fáil would win two of four seats; where it had more than 50% support, three- or five-seat constituencies would give it two of three, or three of five.
- Boundary Delimitation Glossary ACE:The Electoral Knowledge Network. Accessed 4 July 2009.
- "The Constitution Act, 1867 (UK), 30 & 31 Victoria, c 3, Section 51 (1)". Canadian Legal Information Institute. 1 April 1999. Retrieved 25 August 2013.
- "Constitution Of Ireland". Article 16. Retrieved 2 September 2013.
- Forde, Michael; Leonard, David (2013). Constitutional Law of Ireland (3rd ed.). A&C Black. §§21.05–21.08. ISBN 9781847667380. Retrieved 1 October 2018.
- Constituency Commission (2017). "Appendix 2: Statistics relating to recommended Dáil constituencies". Constituency Commission Report 2017: Dáil and European Parliament Constituencies (PDF). Dublin: Stationery Office. p. 66. ISBN 978-1-4064-2952-7.; "Electoral (Amendment) (Dáil Constituencies) Bill 2017: Second Stage". Seanad Éireann debate. Oireachtas. 15 December 2017. Retrieved 2 October 2018.; "Electoral (Amendment) (Dáil Constituencies) Act 2017". electronic Irish Statute Book. 23 December 2017. Retrieved 2 October 2018.
- "Consultation Paper on the Establishment of an Electoral Commission in Ireland" (PDF). Department of the Environment, Community and Local Government (DECLG). 27 January 2015. Retrieved 28 April 2015.
- Parker, A. J. (1986). "Geography and the Irish Electoral System". Irish Geography. 19 (1): 1–14. doi:10.1080/00750778609478835. ISSN 0075-0778.
- Harrop, Martin; Miller, William Lockley (1987). Elections and voters: a comparative introduction. Macmillan Education. p. 65. ISBN 9780333347607.
- "In re Art. 26 of the Constitution and the Electoral (Amendment) Bill, 1961".  I.R. 169. Retrieved 2 September 2013.
- Carolan, Mary (28 November 2017). "Next Dáil 'unconstitutional' if number of TDs not increased". The Irish Times. Retrieved 1 October 2018.; O'Mahony, Conor; Ó Conaill, Seán (27 November 2017). "Not Just a Christmas Election – An Unconstitutional Election?". Constitution Project. UCC. Retrieved 1 October 2018.
- "Calculating future Māori and General Electorates | Electoral Commission". 18 November 2013. Retrieved 10 April 2014.
- A guide to Boundary Delimitation a series of articles from the ACE Project
- Reapportionment and Redistricting in the U.S. — from the ACE Project
- Boundary Delimitation in the Legal Framework of Elections — from the International IDEA publication International Electoral Standards: Guidelines for reviewing the legal framework of elections
- Redistribution Overview from the Australian Electoral Commission
- U.S. House of Representatives — District apportionment 1790 to 2000