The ITM Cup (previously Air New Zealand Cup) replaces the former National Provincial Championship Division One competition. The NPC competition, played across three divisions, was introduced in 1976, with finals introduced in 1992. Twenty seven teams, each representing a provincial union, make up the competition across three divisions.
New Zealand's provincial unions are (from north to south): Northland, North Harbour, Auckland, Counties Manukau, Thames Valley, Waikato, Bay of Plenty, East Coast, Poverty Bay, Hawke's Bay, King Country, Taranaki, Manawatu, Wanganui, Waiararapa-Bush, Horowhenua-Kapiti, Wellington, Nelson Bays, Marlborough, Buller, West Coast, Canterbury, Mid Canterbury, South Canterbury, North Otago, Otago and Southland.
The Super Rugby franchises (Blues, Chiefs, Hurricanes, Crusaders and Highlanders) are linked to their member unions. See
http://en.wikipedia.org/wiki/Super_Rugby_franchise_areas#New_Zealand