population as the South Island ones. Electorates may vary by no more than 5% of the average population size. This has caused the number of list seats in Parliament to decline as the population is experiencing "northern drift" (i.e. the population of the North Island, especially around Auckland, is growing faster than that of the South Island) due both to internal migration and to immigration. Although the New Zealand Parliament is intended to have 120 members, some terms have exceeded this quantity. Overhang seats arise when a party win more seats via electorates than their proportion of the party vote entitles them to; other parties are still awarded the same number of seats that they are entitled to, which results in more than 120 seats in total. In 2005 and 2011, 121 members were elected; 122 members were elected in 2008. History Originally, electorates were drawn up by the Representation Commission based on political and social links, with little consideration for differences in population. Elections for the New Zealand House of Representatives in the 1850s modelled the electoral procedures used for the British House of Commons, which at that time featured both single-member electorates (electorates returning just one MP) and multi-member electorates (electorates returning more than one MP). Each electorate was allocated a different number of MPs (up to three) in order to balance population differences. All electorates used a plurality voting system. From 1881, a special country quota meant that rural seats could contain fewer people than urban seats, preserving improportionality by over-representing farmers. For the 1905 election the multi-member electorates were abolished. The quota system persisted until 1945. Because of the increasing North Island population, the Representation Commission awarded the North Island an additional electoral seat beginning in the 2008 general election. Another new North Island seat was added for the 2014 general election, and again for the 2020 general election (with one new electorate in Auckland). Each time, the need for an additional seat was determined from the results of the most recent New Zealand census, with the seat coming out of the total number of list seats. The total number of list seats has thus declined from 55 to 48 since the introduction of mixed-member proportional voting in the 1996 general election. Naming conventions The Representation Commission determines the names of each electorate following the most recent census. An electorate may be named after a geographic