island in the Strait of Malacca, Riau provinsi (province), Indonesia. It lies just off the eastern coast of Sumatra across a 3-mile- (5-kilometre-) wide channel, opposite Melaka, Malaysia. The island is very low and swampy and circular in shape, with a diameter of about 30 miles (48 km). The climate is hot and humid, and rainfall is heavy most of the year. Rupat Island is sparsely inhabited, and unmanageable seasonal floods make cultivation virtually impossible. Exploration of the interior has thus been difficult, and human habitation is confined to the low, dry coastland. The only major settlement is Batupanjang on the southwestern coast.