The archipelago of Indonesia is strategically located in South East Asia, between the Malay Peninsula and Australia, as the crossroad between the Pacific and Indian Ocean, Indonesia shares borders with Singapore, Malaysia and The Philippines to the north, with Papua New Guinea to the east, with Australia to the south, and with India (Nicobar and Andaman Islands) to the west. Being the largest archipelago in the world, it consists of 17.508 big and small islands. The five main islands are: Sumatra, which is about 473,606 sq. km. in size; the most fertile and densely populated islands-Java/Madura, 132,107 sq. km; Kalimantan, which comprises two-thirds of the island of Borneo and measures 539,460 sq. km; Sulawesi (Celebes), 189,216 sq. km; and Irian Jaya (Papua), 421,981 sq. km, which is part of the world's second largest island, New Guinea. Indonesia's other islands are smaller in size. Bali (5,632 sq.km) is one of the Lesser Sunda Islands, comprising among others: Lombok (4,739 sq.km), Sumbawa (15,600 sq.km), Sumba (11,150 sq.km), Flores and (West) Timor (19,000 sq.km). The territory of the Republic of Indonesia stretches from 6o08' north latitude to 11o15' south latitude, and from 94o45' to 141o05' east longitude. The Indonesian sea area is four times greater than its land area, which is about 1.9 million sq. km. The sea area is about 7.9 million sq. km (including an exclusive economic zone) and constitutes about 81% of the total area of the country.
The archipelago is divided into three groups. The islands of Java, Sumatra and Kalimantan, and the small islands in-between, lie on the Sunda Shelf, which begin on the coasts of Malaysia and Indo China, where the sea depth does not exceed 700 feet. Irian Jaya which is part of the island of New Guinea, and the Aru Islands lie on the Sahul Shelf, which stretches northwards from the Australian coast. Here the sea depth is similar to that of the Sunda Shelf. Located between these two shelves is the transitional zone, comprising the island group of Nusatenggara, Maluku and Sulawesi, where the sea depth reaches 15,000 feet.
Coastal plains have been developed around the islands of Sumatra, Java, Kalimantan and Irian Jaya. 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. The country is predominantly mountainous with some 400 volcanoes, of which 100 are active. The islands are the sight of the earth's two greatest historic volcanic cataclysms, Krakatoa (August 26th, 1883) and Tambora (1815), and each year brings an average of 10 major eruptions. This activity not only destroys but also provides great benefits. The Hindu monuments constructed for over 750 years on Java were for the most part built from cooled lava rock, ideal for carving. The chemical rich ash produced by an eruption covers a wide area of surrounding land; rivers carry ash even farther by way of irrigation canals. Thus Indonesia enjoys some of the most fertile land on the planet. Mountains higher than 9,000 feet are found on the islands of Sumatra (Mt. Leuser and Mt. Kerinci), Java (Mt. Gede, Mt. Tangkubanperahu, Mt. Ciremai, Mt. Kawi, Mt. Kelud, Mt. Semeru and Mt. Raung), Sulawesi (Mt. Lompobatang and Mt. Rantekombala), Bali (Mt. Batur and Mt. Agung), Lombok (Mt. Rinjani) and Sumbawa (Mt. Tambora). The highest mountain is the perpetually snow-capped Mandala Top (15,300 feet) in the Jaya Wijaya mountain range of Irian Jaya (West Papua).
Many rivers flow throughout the country. They serve as useful transportation routes on certain islands, for example, the Musi, Batanghari, Indragiri and Kampar rivers in Sumatra; the Kapuas, Barito, Mahakam and Rejang rivers in Kalimantan; and the Memberamo and Digul rivers in Irian Jaya. On Java, rivers are important for irrigation purposes, i.e., the Bengawan Solo, Citarum and Brantas rivers.
A number of islands are dotted with scenic lakes, like the Toba, Maninjau and Singkarak lakes on Sumatra; the Tempe, Towuti, Sidenreng, Poso, Limboto, Tondano, and Matana lakes on Sulawesi; and the Paniai and Sentani lakes on Irian Jaya.

Indonesian’s terrain is mostly coastal low land while larger islands have interior mountains, covered by dense equatorial tropical rainforest. The country’s lowest point is at Indian Ocean 0 m and its highest point is Puncak Jaya Mount (5,030 m) in Irian Jaya, the only place in the country covered by eternal snow. It is one of the richest countries with natural resources, such as: petroleum, tin, natural gas, nickel, timber, bauxite, copper, fertile soils, coal, gold and silver.