The territory of the Republic of Indonesia stretches from 6°8' north latitude to 11°15' south latitude and from 94°45' to 141°65' east longitude. Its estimated total area is 9.8 million square kilometers, of which 19% is land.
Indonesia's five biggest islands are Sumatra, Java (the most fertile and densely populated island), Kalimantan, Sulawesi and Papua. Papua is part of the world's second biggest island, namely New Guinea.
The Indonesian archipelago is divided into three divisions. The island of Java, Sumatra and Kalimantan, together with the small islands in between, stand on the Sunda Shelf. Papua and the Aru Islands lie on the Sahul Shelf, which stretches northwards from the Australian coast. Located between these two shelves is the group of islands called Nusatenggara, among which are the islands Maluku and Sulawesi.
Coastal plains have been developed around the islands of Sumatra, Java, Kalimantan and Papua. The land area is generally covered by thick tropical rain forests, where fertile soils are continuously replenished by volcanic eruptions like those on the island of Java.
An additional advantage of the island of Java is that its coastal plains are not edged by wide swamps as in the case of Sumatra, Kalimantan and Papua, not bordered by coral reefs as in the case of the island of Sulawesi.
On the island of Sumatra there is plenty of evidence of past volcanic activities, although the ejected material contained acid which makes Sumatra less fertile than Java.