Pacific Ocean, central Pacific, north Pacific, south Pacific

For convenience of description, that part of the Pacific between the tropics of Cancer and Capricorn will be called central Pacific, the area to the north being known as north Pacific, and that south of the tropic of Capricorn, the south Pacific. However, the equator is used to divide the Pacific area into north Pacific and south Pacific by the International Hydrographic Bureau. As previously mentioned, the meridian of 150° west divides the eastern from the western Pacific.

The term South Sea has been loosely used, often for the Pacific south of the equator, but it originated with the Spaniard Balboa, who named the Pacific Ocean at Panama "South Sea." For many years South Sea continued to be applied to anything south of the sailing route followed by the galleons on their voyage from Manila to Acapulco, Mexico. This route passed north of Hawaii in order to avoid the northeast trades and to take advantage of the prevailing westerly winds.

The international date line coincides with the 180° meridian, except for zigzags to give the same date to politically related areas a little distance on either side.

For descriptive purposes the customary divisions of the Pacific islands, including the waters around them, are Melanesia, Micronesia, and Polynesia (see Frontispiece). These names are based on the character of the islands or their native peoples. Melanesia (black islands), named from the complexion of its natives, includes the islands south of the equator and north and northeast of Australia, including New Guinea, the Bismarck Archipelago, and the Solomon, New Hebrides, Admiralty, Santa Cruz, New Caledonia, Loyalty, and Fiji islands. Micronesia (little islands) includes the Marianas, Caroline, Palau, Yap, Marshall, and Gilbert islands. Polynesia (many islands) is a huge triangular area, 5000 miles from north to south and 400 miles from east to west. It extends from Hawaii on the north to New Zealand on the southwest and Easter Island on the southeast. It includes the Marquesas, Tuamotu, Society, Samoa, Tonga, Cook, and other islands and groups. The natives of Fiji are of the Melanesian stock but possess much Polynesian culture.

Oceania commonly refers to the Pacific islands, including New Guinea, and some authorities would include and some exclude Australia and the East Indies.