Polynesia is characterized by a small amount of land spread over a very large portion of the mid and southern Pacific Ocean. Most Polynesian islands and archipelagos, including the Hawaiian Islands and Samoa, are composed of volcanic islands built by hotspots. New Zealand, Norfolk Island, and Ouvéa, the Polynesian outlier near New Caledonia, are the unsubmerged portions of the largely sunken continent of Zealandia. Zealandia is believed to have mostly sunk 23 million years ago and recently resurfaced geologically due to a change in the movements of the Pacific Plate in relation to the Indo-Australian plate, which served to uplift the New Zealand portion. At first, the Pacific plate was subducted under the Australian plate. The Alpine Fault that traverses the South Island is currently a transform fault while the convergent plate boundary from the North Island northwards is called the Kermadec-Tonga Subduction Zone. The volcanism associated with this subduction zone is the origin of the Kermadec and Tongan island archipelagos.
Out of approximately 300,000 or 310,000 square kilometres (117,000 or 118,000 sq mi) of land, over 270,000 km2 (103,000 sq mi) are within New Zealand; the Hawaiian archipelago comprises about half the remainder. The Zealandia continent has approximately 3,600,000 km2 (1,400,000 sq mi) of continental shelf. The oldest rocks in the region are found in New Zealand and are believed to be about 510 million years old. The oldest Polynesian rocks outside of Zealandia are to be found in the Hawaiian Emperor Seamount Chain, and are 80 million years old.
Polynesia is generally defined as the islands within the Polynesian Triangle, although there are some islands that are inhabited by Polynesian people situated outside the Polynesian Triangle. Geographically, the Polynesian Triangle is drawn by connecting the points of Hawaii, New Zealandand Easter Island. The other main island groups located within the Polynesian Triangle are Samoa, Tonga, the Cook Islands, Tuvalu, Tokelau, Niue, Wallis and Futuna and French Polynesia.
There are also small Polynesian settlements in Papua New Guinea, the Solomon Islands, the Caroline Islands, and in Vanuatu. An island group with strong Polynesian cultural traits outside of this great triangle is Rotuma, situated north of Fiji. The people of Rotuma have many common Polynesian traits but speak a non-Polynesian language. Some of the Lau Islands to the southeast of Fiji have strong historic and cultural links with Tonga.