New Zealand is located near the centre of the water hemisphere and is made up of two main islands and a number of smaller islands. The two main islands (the North Island, or Te Ika-a-Māui, and the South Island, or Te Waipounamu) are separated by Cook Strait, 22 kilometres (14 mi) wide at its narrowest point. Besides the North and South Islands, the five largest inhabited islands are Stewart Island, Chatham Island, Great Barrier Island (in the Hauraki Gulf), d'Urville Island (in the Marlborough Sounds) and Waiheke Island (about 22 km (14 mi) from central Auckland).
New Zealand is long and narrow (over 1,600 kilometres (990 mi) along its north-north-east axis with a maximum width of 400 kilometres (250 mi)), with about 15,000 km (9,300 mi) of coastline and a total land area of 268,000 square kilometres (103,500 sq mi). Because of its far-flung outlying islands and long coastline, the country has extensive marine resources. Its exclusive economic zone is one of the largest in the world, covering more than 15 times its land area.
The South Island is the largest landmass of New Zealand and is the 12th largest island in the world. It is divided along its length by the Southern Alps. There are 18 peaks over 3,000 metres (9,800 ft), the highest of which is Aoraki / Mount Cook at 3,754 metres (12,316 ft). Fiordland's steep mountains and deep fiords record the extensive ice age glaciation of this south-western corner of the South Island. The North Island is the 14th largest island in the world and is less mountainous but is marked by volcanism. The highly active Taupo Volcanic Zone has formed a large volcanic plateau, punctuated by the North Island's highest mountain, Mount Ruapehu (2,797 metres (9,177 ft)). The plateau also hosts the country's largest lake, Lake Taupo, nestled in the caldera of one of the world's most active supervolcanoes.
The country owes its varied topography, and perhaps even its emergence above the waves, to the dynamic boundary it straddles between the Pacific and Indo-Australian Plates. New Zealand is part of Zealandia, a microcontinent nearly half the size of Australia that gradually submerged after breaking away from the Gondwanan supercontinent. About 25 million years ago, a shift in plate tectonic movements began to contort and crumple the region. This is now most evident in the Southern Alps, formed by compression of the crust beside the Alpine Fault. Elsewhere the plate boundary involves the subduction of one plate under the other, producing the Puysegur Trench to the south, the Hikurangi Trench east of the North Island, and the Kermadec and Tonga Trenches further north.
New Zealand is part of Australasia, and also forms the south-western extremity of Polynesia. The term Oceania is often used to denote the region encompassing the Australian continent, New Zealand and various islands in the Pacific Ocean that are not included in the seven-continent model.
New Zealand's climate is predominantly temperate maritime (Köppen: Cfb) with mean annual temperatures ranging from 10 °C (50 °F) in the south to 16 °C (61 °F) in the north. Historical maxima and minima are 42.4 °C (108.32 °F) in Rangiora, Canterbury and −25.6 °C (−14.08 °F) in Ranfurly, Otago. Conditions vary sharply across regions from extremely wet on the West Coast of the South Island to almost semi-arid in Central Otago and the Mackenzie Basin of inland Canterbury and subtropical in Northland. Of the seven largest cities, Christchurch is the driest, receiving on average only 640 millimetres (25 in) of rain per year and Wellington the wettest, receiving almost twice that amount. Auckland, Wellington and Christchurch all receive a yearly average of more than 2,000 hours of sunshine. The southern and south-western parts of the South Island have a cooler and cloudier climate, with around 1,400–1,600 hours; the northern and north-eastern parts of the South Island are the sunniest areas of the country and receive about 2,400–2,500 hours. The general snow season is early June until early October, though cold snaps can occur outside this season. Snowfall is common in the eastern and southern parts of the South Island and mountain areas across the country.
The table below lists climate normals for the warmest and coldest months in New Zealand's six largest cities. North Island cities are generally warmest in February. South Island cities are warmest in January.
New Zealand's geographic isolation for 80 million years and island biogeography has influenced evolution of the country's species of animals, fungi and plants. Physical isolation has not caused biological isolation, and this has resulted in a dynamic evolutionary ecology with examples of very distinctive plants and animals as well as populations of widespread species. About 82% of New Zealand's indigenous vascular plants are endemic, covering 1,944 species across 65 genera and includes a single endemic family. The number of fungi recorded from New Zealand, including lichen-forming species, is not known, nor is the proportion of those fungi which are endemic, but one estimate suggests there are about 2,300 species of lichen-forming fungi in New Zealand and 40% of these are endemic. The two main types of forest are those dominated by broadleaf trees with emergent podocarps, or by southern beech in cooler climates. The remaining vegetation types consist of grasslands, the majority of which are tussock.
Before the arrival of humans, an estimated 80% of the land was covered in forest, with only high alpine, wet, infertile and volcanic areas without trees. Massive deforestation occurred after humans arrived, with around half the forest cover lost to fire after Polynesian settlement. Much of the remaining forest fell after European settlement, being logged or cleared to make room for pastoral farming, leaving forest occupying only 23% of the land.
The forests were dominated by birds, and the lack of mammalian predators led to some like the kiwi, kakapo, weka and takahē evolving flightlessness. The arrival of humans, associated changes to habitat, and the introduction of rats, ferrets and other mammals led to the extinction of many bird species, including large birds like the moa and Haast's eagle.
Other indigenous animals are represented by reptiles (tuatara, skinks and geckos), frogs, spiders, insects (weta) and snails. Some, such as the tuatara, are so unique that they have been called living fossils. Three species of bats (one since extinct) were the only sign of native land mammals in New Zealand until the 2006 discovery of bones from a unique, mouse-sized land mammal at least 16 million years old. Marine mammals however are abundant, with almost half the world's cetaceans (whales, dolphins, and porpoises) and large numbers of fur seals reported in New Zealand waters. Many seabirds breed in New Zealand, a third of them unique to the country. More penguin species are found in New Zealand than in any other country.
Since human arrival, almost half of the country's vertebrate species have become extinct, including at least fifty-one birds, three frogs, three lizards, one freshwater fish, and one bat. Others are endangered or have had their range severely reduced. However, New Zealand conservationists have pioneered several methods to help threatened wildlife recover, including island sanctuaries, pest control, wildlife translocation, fostering, and ecological restoration of islands and other selected areas.