Western Indonesia

The region comprising the other 21 provinces in Sumatra, Java, and Kalimantan is known as Western Indonesia.^[1][2]

Western Indonesia has a land border with East Malaysia to the North and Peninsular Malaysia to the West

Military action by the Dutch launched on 20 July 1947 against areas controlled by the Indonesian republicans, Operation Product, resulted in the Dutch regaining control of West and East Java, the areas around Medan, Palembang and Padang in Sumatra. The United Nations called for a ceasefire, and negotiations between the two sides led to the Renville Agreement of January 1948, with a ceasefire along the "Van Mook Line", which connected the most advanced Dutch positions. The Dutch then established states in the areas they had reoccupied, including East Sumatra (December 1947), Madura and West Java (February 1948), South Sumatra (September 1948) and East Java (November 1948). The leaders of these regions then established the Federal Consultative Assembly.

A second Dutch military action, Operation Kraai, aimed at destroying the Republic, was launched on 18 December 1948. Despite recapturing the major cities of Java, including the republican capital of Yogyakarta, and all of Sumatra except Aceh in the far north, it triggered the protest resignation of the cabinets of the State of East Indonesia and Pasundan (West Java) and the Sultan of Yogyakarta from his position as regional head.

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]

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.

Below are the top 13 provinces in Western Indonesia ranked by GDP in 2019:

Rank	Province	Region	GDP (in billion Rp)	GDP nominal	GDP PPP
				(in billion $)	(in billion $)
-	Indonesia	South East Asia	16,073,257	1,136.72	3,329.17
1	Jakarta	Java	2,840,828	200.91	588.42
2	East Java	Java	2,352,425	166.37	487.27
3	West Java	Java	2,125,158	150.30	440.19
4	Central Java	Java	1,362,457	96.35	282.18
5	North Sumatra	Sumatra	801,733	56.70	166.06
6	Riau	Sumatra	765,198	54.12	158.51
7	Banten	Java	664,963	47.03	137.74
8	East Kalimantan	Kalimantan	653,677	46.23	135.40
9	South Sumatra	Sumatra	455,233	32.19	94.28
10	Lampung	Sumatra	360,664	25.51	74,71
11	Riau Islands	Sumatra	268,080	18.96	55.53
12	West Sumatra	Sumatra	246,423	17.42	51.01
13	Jambi	Sumatra	217,712	15.40	45.10

In 2012, the DMO was 24.72%. Starting from 2014, no low-grade coal exports are allowed, so the upgraded brown coal process that cranks up the calorie value of coal from 4,500 to 6,100 kcal/kg will be built in South Kalimantan and South Sumatra.^[5][6][7] Major Japanese factories are concentrated east of Jakarta with high concentrations in Bekasi, Cikarang and Karawang, West Java.

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:

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][a]}

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

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]

• Regions of Indonesia
• Eastern Indonesia

• Simons, Gary F.; Fennig, Charles D. (2018). "Indonesia". Ethnologue: Languages of the World, Twenty-first edition. SIL International. Archived from the original on 26 June 2019. Retrieved 20 September 2018.
• Zein, Subhan (2020). Language Policy in Superdiverse Indonesia. New York and London: Routledge. ISBN 9780367029548.