The northern of the two main islands of New Zealand, centred around NZTM 1865000E, 5674000N.
The name North Island has been in long term and common usage for over a century. The island has had another English name historically - New Ulster. Early naming of the Northern and Southern Islands was recorded by Hobson in the Proclamation of Sovereignty of 21 May 1840. Hobson had intended to use the native names as per Cook’s chart, but Colenso inserted ‘the Nothern Island’ and ‘the Middle Island’. The name for Nothern Island was later corrected by Hobson’s Proclamation of 13 May 1841 to Northern Island. The Royal Charter of 1840 was received in New Zealand in early 1841 and it named the islands New Ulster (for the North Island), New Munster (for the South Island) and New Leinster (for Stewart Island / Rakiura), with Royal sanction and the gazette notice using these names. Since Royal Charters are perpetual, the names New Ulster, New Munster and New Leinster arguably have some legal standing (but not as Geographic names under the current NZGB Act 2008). They have not been used for the island names since 1841, though they did survive as provincial names up until 1853. Assigning North Island as an alternative name made official under the NZGB Act 2008, is an action that effectively overrides the Royal Charter by bringing the name within the statutory place naming framework empowered by Parliament in the NZGB Act 2008.
LINZ File Reference: GES-N15-07-05/875. See http://www.linz.govt.nz/placenames/consultation-decisions/a-to-z/north-island