Geography

Indonesia is situated in Southeast Asia, in the Malay Archipelago between the Indian Ocean and the Pacific Oceans. It is in a strategic location astride or along major sea lanes from Indian Ocean to Pacific Ocean. Indonesia's 17,508 islands, about 6,000 of which are inhabited, are scattered around the equator. The five main islands are Java, Sumatra, Kalimantan (the Indonesian part of Borneo), New Guinea (shared with Papua New Guinea) and Sulawesi. Indonesia borders Malaysia on the island of Borneo (Indonesian, Papua New Guinea on the island of New Guinea and East Timor on the island of Timor. The capital Jakarta is on Java and is the nation's largest city, followed by Surabaya, Bandung, Medan, and Semarang.

At 1,919,440 sq km (741,050 sq mi), Indonesia is the world's sixteenth-largest country in terms of land area, and is approximately the same size of Mexico. Its population density is 117 people per square kilometre - about half that of the UK.

At 4,884 metres (12,405 feet), Puncak Jaya in Papua is Indonesia's highest peak and Lake Toba in Sumatra its largest lake with an area of 1,145 sq km (442sq m). The country's largest rivers are in Kalimantan and include the Mahakam, and Barito. With their sources in the island's central massif, they meander through swamps to the sea allowing communication and transport between settlements built along their edges.

Mountains

Mountains ranging between 3,000 and 3,800 metres above sea level can be found on the islands of Sumatra, Java, Bali, Lombok, Sulawesi and Seram. The country's tallest mountains are located in the Jayawijaya Mountains and the Sudirman Mountains in Irian Jaya. The highest peak, Puncak Jaya, also known as Mount Carstenz, which reaches 4,884 metres, is located in the Sudirman Mountains.

Volcanoes

Its location on the edges of three tectonic plates, specifically the Pacific, Eurasian, and Australian plates, makes Indonesia a site of numerous volcanoes and frequent earthquakes. Indonesia has at least 66 volcanoes, including Krakatoa and Tambora both famous for their devastating eruptions in the nineteenth century. The eruption of the Toba supervolcano approximately 71,500 years ago was one of the largest eruptions known and a global catastrophe. Between 1972 and 1991 alone, twenty-nine volcanic eruptions were recorded, mostly on Java. The most violent volcanic eruptions in modern times occurred in Indonesia. In 1815 a volcano at Gunung Tambora on the north coast of Sumbawa, Nusa Tenggara Barat Province, claimed 92,000 lives and created 'the year without a summer' in various parts of the world. In 1883 Krakatau in the Sunda Strait, between Java and Sumatra, erupted and some 36,000 West Javans died from the resulting tidal wave. The sound of the explosion was reported as far away as Turkey and Japan. For almost a century following that eruption, Krakatau was quiet, until the late 1970s, when it erupted twice. Volcanic ash, however, is a major contributor to the high agricultural fertility that has historically sustained significantly high population density on the islands of Java and Bali.

Recent disasters due to seismic activity include the tsunami in Aceh in 2004 and the Yogyakarta earthquake in 2006.

Geographic Regions

Indonesia's total land area is 1,919,317 square kilometres. Included in Indonesia's total territory is another 93,000 square kilometres of inlands seas (straits, bays, and other bodies of water). The additional surrounding sea areas bring Indonesia's generally recognised territory (land and sea) to about 5 million square kilometres. The government, however, also claims an exclusive economic zone, which brings the total to about 7.9 million square kilometres.

Indonesia is a huge archipelagic country extending 5,120 kilometres from east to west and 1,760 kilometres from north to south. It encompasses as many as 18,000 islands, only 6,000 of which are inhabited. There are five main islands (Sumatra, Java, Kalimantan, Sulawesi, and Irian Jaya), two major archipelagos (Nusa Tenggara and the Maluku Islands), and sixty smaller archipelagos. Three of the islands are shared with other nations:

• Timor is shared with East Timor
• Irian Jaya shares the island of New Guinea with Papua New Guinea
• Kalimantan (known in the colonial period as Borneo, the world's third largest island) is shared with Malaysia and Brunei

The Greater Sunda Islands

Geographers have conventionally grouped Sumatra, Java (and Madura), Kalimantan (formerly Borneo), and Sulawesi (formerly Celebes) 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 Irian Jaya (formerly Irian Barat or West New Guinea), 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 metres or less. Between these two shelves lie Sulawesi, Nusa Tenggara (also known as the Lesser Sunda Islands), and the Maluku Islands (or the Moluccas), which form a second island group where the surrounding seas in some places reach 4,500 metres in depth. The term Outer Islands is used inconsistently by various writers but it is usually taken to mean those islands other than Java and Madura.

Nusa Tenggara

Nusa Tenggara consists of two strings of islands stretching eastward from Bali toward Irian Jaya. 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

The Maluku Islands (or Moluccas) are geologically among the most complex of the Indonesian islands. They are located in the northeast sector of the archipelago, bounded by the Philippines to the north, Irian Jaya to the east, and Nusa Tenggara to the south. The largest of these islands include Halmahera, Seram, and Buru, all of which rise steeply out of very deep seas. This abrupt relief pattern from sea to high mountains means that there are very few level coastal plains.

Geographers believe that the island of New Guinea, of which Irian Jaya 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. Irian Jaya's mountains range some 650 kilometres east to west, dividing the province between north and south.

Time Zones

The archipelago stretches across three time zones:

• Western Indonesian Time - seven hours in advance of Greenwich Mean Time (GMT) - includes Sumatra, Java, and eastern Kalimantan
• Central Indonesian Time - eight hours head of GMT - includes western Kalimantan, Nusa Tenggara, and Sulawesi
• Eastern Indonesian Time - nine hours ahead of GMT - includes the Malukus and Irian Jaya

The boundary between the western and central time zones - established in 1988 - is a line running north between Java and Bali through the center of Kalimantan. The border between central and eastern time zones runs north from the eastern tip of Timor to the eastern tip of Sulawesi.