Geology

The main islands of Sumatra, Java, Madura, and Kalimantan lie on the Sunda Plate. Indonesia has relatively high tectonic and volcanic activities. It lies on the convergence between the Eurasian, Indo-Australian, Pacific, and Philippine Sea Plate. The Sunda megathrust is a 5,500 km long fault located off southern coasts of Sumatra, Java and Lesser Sunda Islands, where the Indo-Australian Plate is thrusting northeastward towards the subducting Sunda Plate.Tectonic movement in this fault is responsible for the creation of the Sunda Trench, and mountain ranges across Sumatra, Java.^[3] Mount Merapi, located in the Java portion of the megathrust, is the most active volcano in Indonesia and is designated as one of world's Decade Volcanoes due to the hazard it poses to the surrounding populated areas.^[4]

Ecology

Borneo is the third largest island in the world and the native vegetation was mostly Borneo lowland rain forests although much of this has been cleared with wildlife retreating to the Borneo montane rain forests inland. Kalimantan and Sumatra, experience only slight differences in rainfall and temperature between the seasons, whereas others, such as Nusa Tenggara, experience far more pronounced differences with droughts in the dry season, and floods in the wet. Rainfall in Indonesia is plentiful, particularly in West Sumatra, Northwest Kalimantan, West Java.

Population

Jakarta is the largest city and the only megacity in Indonesia, with a population of 10.70 million. As a primate city, Jakarta is nearly four times larger than the second largest city Surabaya. Jakarta's status is unique compared to other cities in Indonesia, since it is technically a province with a city management. It is subdividied into five administrative cities and an administrative regency, which are not self-governed (without municipal council nor government budget). All five of Jakarta's satellite cities also have passed one million mark in population, with the largest one being Bekasi.

The other largest cities by region include Medan (Sumatra, also the largest outside of Java), Samarinda (Kalimantan).

Below are the populations of each provinces which make up the total population of Western Indonesia:

Languages

Indonesia recognizes only a single national language, and indigenous languages are recognized at the regional level, although policies vary from one region to another. For example, in the Special Region of Yogyakarta, the Javanese language is the region's official language along with Indonesian.^[8] The next most widely spoken regional languages in the country are Sundanese, local Malay, and Minangkabau. There are hundreds of indigenous languages spoken in Indonesia. Most of them are locally used indigenous languages,^[9] a category of languages referring to those spoken at the local, regional level, spoken by a small number of people, ranging from a few to a few thousands of people. These include small languages such as Benggoi, Mombum and Towei.^{[10][page needed]} Other languages are spoken at the regional level to connect various ethnicities. For this reason, these languages are known as regional lingua francas (RLFs). According to Subhan Zein, there are at least 43 RLFs in Indonesia, categorized into two types: Malayic RLFs and Non-Malayic RLFs. The former refers to a group of regional lingua francas that are thought of as indigenised varieties of Malay or Indonesian. These include such languages like Banjar Malay among others. The latter refers to regional lingua francas that are not associated with Malay or Indonesian, like Iban.^{[11][10][page needed][lower-alpha 1]}

The population numbers given below are of native speakers, excepting the figure for Indonesian, which counts its total speakers.

Religion

Religion was a census variable in the 1961, 1971, 1980, 1990, 2000, and 2010 and in various intercensal surveys. Being deemed divisive, the 1961 census data regarding religion was not published. In 1971, three groups of Christians were recorded: Catholic, Protestant and other. The U.N. Demographic Yearbook 1979 only lists data collectively for all Christians. In the 2000 census, only Catholics and Protestants were available as categories.^[14]

Religious composition by ethnic group^[15]