Why are Australia, Indonesia, the Philippines, and Japan usually excluded from the Pacific Islands region?

The classification of the Pacific Islands as a distinct geographic region conventionally excludes Australia, Indonesia, the Philippines, and Japan based on established ethnogeographic and physiographic conventions.

While these nations are located within or adjacent to the Pacific Ocean, they are typically categorized separately due to their continental status or their strong historical, cultural, and political associations with the Asian continent. In contrast, the Pacific Islands region is defined by its specific groupings of Melanesia, Micronesia, and Polynesia.

Furthermore, from a geological perspective, the region is often delineated by the Andesite Line. This line separates the basaltic volcanic islands of the central and eastern Pacific from the western Pacific margin, where islands are formed primarily of metamorphosed rocks, sediment, and andesitic volcanic material. Consequently, while the broader term Oceania can encompass these areas in its widest definition, the term Pacific Islands is used more strictly to refer to the specific island groups mentioned above.1