Indonesia is an archipelagic country extending 5,120 kilometers from east to west and 1,760 kilometers from north to south.
It has 17508 islands, only 6,000 of which are inhabited. There are five main islands ( Sumatra , Java , Borneo , Sulawesi , and New Guinea ), two small archipelagos ( Nusa Tenggara and the Maluku Islands ), and sixty smaller archipelagos.
Three of the islands are shared with other nations; Borneo (Indonesia's region is called Kalimantan ) is shared with Malaysia and Brunei , Timor is shared with East Timor , and Papua shares the island of New Guinea with Papua New Guinea . Indonesia's total land area is 1,919,317 square kilometers. Included in Indonesia's total territory is another 93,000 square kilometers of inlands seas ( straits , bays , and other bodies of water).
The additional surrounding sea areas bring Indonesia's generally recognized territory (land and sea) to about 5 million square kilometers.
The government, however, also claims an exclusive economic zone, which brings the total to about 7.9 million square kilometers.
Geographers have conventionally grouped Sumatra, Java (and Madura), Kalimantan (in Borneo island), and Sulawesi in the Greater Sunda Islands.
These islands, except for Sulawesi, lie on the Sunda Shelf--an extension of the Malay Peninsula and the Southeast Asian mainland. Far to the east is Papua , which takes up the western half of the world's second largest island--New Guinea--on the Sahul Shelf.
Sea depths in the Sunda and Sahul shelves average 200 meters or less. Between these two shelves lie Sulawesi, Nusa Tenggara (also known as the Lesser Sunda Islands ), and the Maluku Islands , which form a second island group where the surrounding seas in some places reach 4,500 meters in depth.
Mountains ranging between 3,000 and 3,800 meters above sea level can be found on the islands of Sumatra, Java, Bali, Lombok, Sulawesi, and Seram. The country's the highest mountains are located in the Jayawijaya Mountains and the Sudirman Mountains in Papua. The highest peak, Puncak Jaya , also known as Mount Carstenz, which reaches 4,884 meters, is located in the Sudirman Mountains.
Nusa Tenggara consists of two strings of islands stretching eastward from Bali toward Papua. The inner arc of Nusa Tenggara is a continuation of the chain of mountains and volcanoes extending from Sumatra through Java, Bali, and Flores, and trailing off in the Banda Islands. The outer arc of Nusa Tenggara is a geological extension of the chain of islands west of Sumatra that includes Nias, Mentawai, and Enggano. This chain resurfaces in Nusa Tenggara in the ruggedly mountainous islands of Sumba and Timor.
The Maluku Islands are geologically among the most complex of the Indonesian islands. They are located in the northeast of the archipelago, nearly by the Philippines to the north, Papua to the east, and Nusa Tenggara to the south. The largest of these islands include Halmahera, Seram and Buru, all of which have very deep seas..
Geographers believe that the island of New Guinea, of which Papua is a part, may once have been part of the Australian continent. The breakup and tectonic action created both towering, snowcapped mountain peaks lining its central east-west spine and hot, humid alluvial plains along the coast of New Guinea. Papua's mountains range some 650 kilometers east to west, dividing the region between north and south.