Almost completely surrounded by mountain ranges (including the Himalayas in the south and the Kunlun in the north), Tibet is largely a plateau averaging c.16,000 ft (4,880 m) in height. Many of the mightiest rivers of E Asia, especially the Chang (Yangtze), the Mekong, and the Thanlwin, rise in Tibet; the most important is the navigable Yarlung Zangbo (the Brahmaputra), which follows an easterly course through S Tibet. North of the Yarlung Zangbo are many salt lakes, the largest being Nam Co (Tengri Nor) in the east.
The indigenous inhabitants are of Mongolian stock and speak a Tibeto-Burman language. There are also substantial numbers of Han and other Chinese, especially in E Tibet and in urban areas; the number of non-Tibetans has increased significantly since 1990. Before the unsuccessful revolt of 1959 (see History ), many city dwellers were Tibetan Buddhist monks, who may have comprised as much as one sixth of the country's male population. The chief figures of Tibetan Buddhism, the Dalai Lama and the Panchen Lama (or Tashi Lama, for the lamastery at Tashi Lumpo), were at least the nominal heads of the Tibetan government. In general, the former administration was equally divided between lamas and the feudal aristocracy.