In Australia, a redistribution is the process of redrawing the boundaries of electoral divisions for the House of Representatives arising from changes in population and changes in the number of representatives. There is no redistribution for the Senate as each State constitutes a division, though with multiple members. The Australian Electoral Commission (AEC), an independent statutory authority, oversees the apportionment and redistribution process for federal divisions, taking into account a number of factors. Politicians, political parties and the public may make submissions to the AEC on proposed new boundaries, but any interference with their deliberations is considered a serious offence.
Section 24 of the Constitution of Australia specifies that the number of members of the House of Representatives in each state is to be calculated from their population, although each state is entitled to a minimum of five members regardless of population. This minimum condition currently only applies to Tasmania, the smallest state. Representation of territories has been specified by subsequent laws. After the number of members for each state and territory is determined, in a process called apportionment or determination, the state and territory is divided into that number of electoral divisions.
A redistribution (sometimes called redrawing or "revision") of the geographic boundaries of divisions in a state or territory takes place when an apportionment determination results in a change in the number of seats to which a state or territory is entitled, at least once every seven years, or sooner when the AEC determines that population shifts within a state or territory have caused some seats to have too many or too few voters. The Commonwealth Electoral Act 1918 requires that all electoral divisions within a state or territory have approximately an equal numbers of enrolled voters. The Commonwealth Electoral Act (No. 2) 1973 reduced the allowed variation of electors in each division to 10% of the state or territory's average, down from 20%. New boundaries apply only to general elections held after the redistribution process has been completed, and by-elections are held on the previous electoral boundaries.
Each state and territory has its own commission which follows similar but not identical processes and principles for determining electoral boundaries and conducting elections within their jurisdiction, and those of local governments.
Redistribution triggers
Under Section 59 of the Commonwealth Electoral Act 1918, a redistribution of State divisions is required or triggered in three circumstances: if there has been a change in the number of parliamentary representatives to which a State or Territory is entitled, due to a change in population or an increase in the overall number of members, subject to the minimum number of divisions in original States if the number of electors in more than one third of the divisions in a State or one of the divisions in the ACT or Northern Territory deviates from the average State divisional enrolment by more than 10% for a period of more than two months (malapportionment) if seven years has elapsed since the previous redistribution
Total number of members
Section 24 of the Constitution specifies that the total number of members of the House of Representatives shall be "as nearly as practicable" twice as many as the number of members of the Senate. There is presently a total of 76 senators: 12 senators from each of the six states and two from each of the two autonomous internal territories (the Australian Capital Territory and the Northern Territory). Since the 2019 federal election, there have been 151 members of the House of Representatives.
The total number of members of the House of Representatives, and consequently electorates, has increased from time to time. Every time there is an increase in the number of members, a redistribution is required to be undertaken, except in Tasmania which has always had the constitutional minimum number of five members. At the first federal election there were 65 members of the House of Representatives. In 1949, the number was increased from 74 to 121 (excluding the Australian Capital Territory and the Northern Territory), and in 1984 it was increased from 125 to 148. Following the 2017 apportionment, the total number of members increased from 150 to 151.