Phuket is the biggest island in Thailand, located in the Andaman Sea of southern Thailand. The island is mostly mountainous with a mountain range in the west of the island from the north to the south. The mountains of Phuket form the southern end of the Phuket mountain range, which ranges for 440 kilometres from the Kra Isthmus. Although some recent geographical works refer to the sections of the Tenasserim Hills in the isthmus as the "Phuket Range", these names are not found, however, in classical geographic sources. In addition, the name Phuket is relatively recent having previously been named Jung Ceylon and Thalang. The highest elevation of the island is usually regarded as Khao Mai Thao Sip Song (Twelve Canes), at 529 metres above sea level. However it has been reported by barometric pressure readings that there is an even higher elevation (with no apparent name), of 542 metres above sea level, in the Kamala hills behind Kathu waterfall.