Borneo, which is called Kalimantan (Malaysian: Borneo) in Indonesia, has an area of 743,330 km2, making it the third largest island (after Greenland and New Guinea) in the world. It is located in the middle of the Indonesian archipelago, and is politically divided between Indonesia, Malaysia and Brunei. It belongs to the group of Great Sunda Islands. Approximately 73% of the island is Indonesian territory.
The coast of the island is relatively inaccessible due to the swamp forests of mangroves, which results in a low population of the coast. Even most rivers are not (due to sea sediments) accessible from the sea. Large areas are still covered with dense rainforests.
From the extreme northern part of the island, Cap Sampanmangio, to the northwestern end of Cap Datu, there is a long mountain range. Several groups of hills surrounded by plains rise on the central plateau. The highest point on the island is the top of Kinabalu (4,101 meters above sea level) and is located in the northeast. Granite and slate hills are mostly in the western part of Borneo. The largest river system is the Capuas in West Kilimantan, with a length of 1000 km. The other main rivers are the Mahakam in East Kalimantan (920 km), the Barito in South Kalimantan (900 km), the Rajang in Sarawak (565 km) and the Kinabatangan in Sabah (560 km). The coast is 4,971 km long. It is not very indented, but there are still some good and safe bays with ports. Before sea levels rose at the end of the last ice age, Borneo was part of the Asian landmass, forming with Java and Sumatra the mountainous areas of the peninsula that stretched east of present-day Indochina. The South China Sea and the Gulf of Thailand now cover the former lowland parts of the peninsula. The deeper waters that separate Borneo from neighboring Sulawesi prevented a land connection with the island, creating a separation known as the Wallace line between the biological regions of Asia and Australia-New Guinea. West of Borneo are the Anamba Islands.
Borneo's climate is distinctly tropical. The average temperature fluctuates between 27.7 ° C in July and 26.7 ° C in October. Most of the southern part of Borneo has a pronounced dry and one rainy period, while in the north there are two such periods.
Borneo has a population of 19,804,064 (as of 2010) and thus a population density of only 26.65 inhabitants per km².