Indonesia comprises three time-zones. These are the Indonesia Western Time, Indonesia Eastern Time and, Indonesia Central Time. Though there are four time-zones in the Indonesian archipelago from Aceh to western Papua; however, in Indonesia, only the above three are recognized.
The Indonesia Western Standard Time, which is seven hours ahead of the GMT, and is used in Sumatra and the surrounding islands. It is also observed in major cities such as Jambi, Padang, Banda Aceh, Bandar Lampung, Medan, Pekanbaru, Batam, and Palembang. It is also used in provinces that are located in Java, and includes major cities such as Jakarta, Yogyakarta, Bandung, Semarang, and Surabaya. The provinces of Central Kalimantan and West Kalimantan also use the Western Time Zone. Important cities in this region are Sampit, Pontianak, and Palangkaraya.
The Indonesia Eastern Standard Time, which is nine hours ahead of GMT, is observed in the Maluku Islands and the provinces in Western New Guinea. The major cities in this region are Ternate City, Ambon City and Tidore in the Maluku Islands; and Biak, Merauke, and Jayapura in Western New Guinea.
The Indonesia Central Standard Time, which is eight hours ahead of GMT, is observed in the provinces located in the island of Sulawesi, provinces in the Lesser Sunda Islands, and the three provinces of East Kalimantan, North Kalimantan, and South Kalimantan in the Kalimantan island. Major cities falling within this time zone are Manado, Makassar, Gorontalo, and Palu (provinces in the island of Sulawesi); Kupang, Denpasar, and Mataram (Lesser Sunda Islands); and Samarinda, Balikpapan, Tarakan, and Banjarmasin (Kalimantan Island).