Brunei Darussalam lies on the northwest coast of Borneo island Where it faces the South China Sea. With a land area of 5,765 square kilometres, it shares a common border with Sarawak, an east Malaysian state, which divides Brunei Darussalam into two, The eastern part is the Temburong District while the western portion consists of Brunei-Muara, Tutong and Belait districts. The 570-sq.km. Brunei-Muara District, where the capital, Bandar Seri Begawan is located, is the smallest, but the most important and populous of the four districts. The 1166 sq. km. Tutong District, the third largest, is home to indigenous groups like the Tutong, the Kedayan, Dusun and Iban. The Belait District, the centre of the oil and gas industries, is about 100 lcrns. From the capital. Hilly lowlands, swampy plains and alluvial valleys dominate the BruneiMuara, Tutong and Belait districts in the larger western portion of the sultanate.