Indonesia, known formally as the Republic of Indonesia, is an island nation composed of a total of 17,508 islands extending 5,150 km/3,200 miles between the Pacific Ocean and the Indian Ocean occupying an area between Asia and Australia.
The country is made up of five major islands and approximately 30 smaller groups of islands. However, only approximately 6,000 of those islands are inhabited.
It is a country of many mountains, some of which are over 4000 metres/13,123 feet. A significant percentage of them are active volcanoes. Some of the habitats here are tropical rainforests, jungles, and swampy mangrove areas. 
Islands of Indonesia
Major Island Groups
Indonesia has 5 major, or main, island groups.
Sumatra comprises 473,606 sq. km/182,860 sq miles in area.
Java / Madura
Java / Madura comprises 132,107sq. km/51,006 sq miles in area.
West Java is the home of the Gede Pangrango National Park with all it has to offer.
Kalimantan with 539,460 sq. km/20,8286 sq miles in area, makes up 2/3 of the island of Borneo.
Sulawesi comprises 189,216 sq. km/73,056 sq miles in area.
Irian Jaya - Maluku Islands - Moluccas
This island group, like others in Indonesia goes by differing names. They have been seen as Irian Jaya, Maluku Islands, and the Moluccas with the Moluccas broken down into North Maluku and Maluku.
Whatever you choose to call it, it comprises 421,981 sq. km/162927 sq miles in area, is a part of the island of New Guinea.
- Embassy of the Republic of Indonesia - https://www.embassyofindonesia.org/index.php/basic-facts/
- BirdForum Opus contributors. (2021) Indonesia. In: BirdForum, the forum for wild birds and birding. Retrieved 12 May 2021 from https://www.birdforum.net/wiki/Indonesia