Indonesia is the largest archipelago in the world. It consists of five major islands and about 30 smaller groups. The new figure for the total number of islands is more than 17,000 according to the Indonesian Naval Hydro-Oceanographic office. This figure is increased from the official figure so far known, that is 13,667. The archipelago is on a crossroad between two oceans, the Pacific and the Indian, and bridges two continents, Asia and Australia. This strategic position has always influenced the cultural, social, political and economic life of the country.

The territory of the Republic of Indonesia stretches from 6 degrees 8 feet north latitude to 11 degrees 15 feet 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 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, 189,216 sq. km.; and Irian Jaya, 421,981 sq. km. which is part of the world's second largest island, New Guinea. Indonesia's other islands are smaller in size.

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 island group of Nusa Tenggara, 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 climate and weather of Indonesia is characterized by two tropical seasons, which vary with the equatorial air circulation (the Walker circulation) and the meridian air circulation (the Hardley circulation). The displacement of the latter follows the north-south movement of the sun and its relative position from the earth, in particular from the continents of Asia and Australia, at certain periods of the year. These factors contribute to the displacement and intensity of the Inter-Tropical Convergence Zone (ITCZ) which is an equatorial trough of low pressure that produces rain. Thus, the west and east monsoons, or the rainy and dry seasons, are a prevalent feature of the tropical climate.

The Main Seasons

The climate changes every six months. The dry season (June to September) is influenced by the Australian continental air masses; while the rainy season (December to March) is the result of the Asian and Pacific Ocean air masses. The air contains vapor which precipitates and produces rain in the country. Tropical areas have rains almost the whole year through. However, the climate of Central Maluku is an exception. The rainy season is from June to September and the dry season from December to March. The transitional periods between the two seasons are April to May and October to November.

Temperature and Humidity

Due to the large number of islands and mountains in the country, average temperatures may be classified as follows:

coastal plains : 28 degrees Celsius

inland and mountain areas : 26 degrees Celsius

higher mountain areas : 23 degrees Celsius, varying with the altitude.

Being in a tropical zone, Indonesia has an average relative humidity between 70% and 90%, with a minimum of 73% and a maximum of 87%.


When independence was proclaimed and sovereignty gained, Indonesia had to enact laws to govern the seas in accordance with the geographic structure of an archipelago state. This, however, did not mean that the country would bar international passage. The laws were necessary instruments for the unity and

national resilience of the country, with a territory that embraces all the islands, the islets and the seas in between.

In view of the country's susceptibility to foreign intervention from the sea and for domestic security reasons, on December 13, 1957, the Indonesian Government issued a declaration on the territorial waters of the Republic. It stated that all the waters surrounding and between the islands in the territory came within Indonesia's sovereignty. It also determined that the country's territorial water limit was 12 miles, measured from a straight baseline drawn from the outermost points of the islands.

In the past, archipelago states like Indonesia have unilaterally determined their 200 mile Exclusive Economic Zones. Today, such economic zones are confirmed by the International Convention on the Law of the Seas, which was ratified by the Indonesian Government on October 18, 1983, by Act No. 5 of the same year. This is the legal basis of the Indonesian-Exclusive Economic Zone.


The country is predominantly mountainous with some 400 volcanoes, of which 100 are active. Mountains higher than 9,000 feet are found on the islands of Sumatra (Mr. Leuser and Mr. 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.

Recorded eruptions of volcanoes over the last two decades are: Sumatra - Dempo 1973, and 1974, Merapi 1978, Sorik Merapi 1989, Kerinci 1990; Sunda Strait Anak Krakatau 1978 and 1979; Java - Bromo 1972, Merapi 1972 and 1976, Raung 1978, Semeru 1978 and 1979, Butak Petarangan (Sinila and Sigludar) 1979; Paluweh - Rokatenda 1978, Galunggung 1982, Slamet 1988, Kelud 1990; Sulawesi - Lokon 1978, 1979 and 1991, Siau - Karangetang 1978 and 1979, Colo 1983, Soputan 1989; Maluku - Dukono 1978, Gamalama Kie Besi 1987, Banda Api 1988; East Nusa Tenggara - Lewotobi laki - laki 1990.


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. All 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.


As of January 1, 1988, Indonesia's three time zones have been changed as shown on the map below:

1. Western Indonesia Standard Time equals GMT plus 7 hours (meridian 105 degrees East), covering all provinces in Sumatra and Java, and the provinces of West and Central Kalimantan.

2. Central Indonesia Standard Time equals GMT plus 8 hours (meridian 120 degrees East), covering the provinces of East and South Kalimantan, all provinces in Sulawesi, and the provinces of Bali, West and East Nusatenggara and East Timor.

3. Eastern Indonesia Standard Time equals GMT plus 9 hours (meridian 135 degrees East), covering the provinces of Maluku and Irian Jaya.

(Source: INDONESIA 1995 An Official Handbook)

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