In 1832 Jules Dumont d'Urville, a French naval officer and explorer, proposed to the Geographical Society of Paris that the Pacific be divided into Polynesia, Micronesia and Melanesia. The three names have been in use ever since. His criteria were not the same in each case: Micronesia was defined by the size of the islands, Polynesia by their number, and Melanesia by the appearance of the inhabitants, the name meaning the black islands. That is the basis of this grouping and the atlas states it on the row.
The area it covers, New Guinea, the Solomons, Vanuatu, New Caledonia and Fiji, is among the most linguistically diverse places on earth: more than a thousand languages, belonging to Austronesian and to a large number of unrelated families collectively called Papuan for want of anything better. There is no common ancestry and no common culture. The category survives because it is administratively convenient, because regional institutions have grown up around it, and because a name in use for two centuries is hard to dislodge, not because anything holds it together. Fiji sits awkwardly inside it, having been assigned to Melanesia on appearance while its language belongs with the Polynesian group's nearest relatives, which is as clear a demonstration as the scheme offers that its criteria and the evidence do not line up.