The Tibetan Plateau, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau or as the Himalayan Plateau in India, is a vast elevated plateau in Central Asia and East Asia, covering most of the Tibet Autonomous Region, most of Qinghai, Northwestern Yunnan, Western half of Sichuan, Southern Gansu provinces in Western China, the Indian regions of Ladakh and Lahaul and Spiti as well as Bhutan. It stretches approximately 1,000 kilometres north to south and 2,500 kilometres east to west. It is the world's highest and largest plateau above sea level, with an area of 2,500,000 square kilometres. With an average elevation exceeding 4,500 metres and being surrounded by imposing mountain ranges that harbor the world's two highest summits, Mount Everest and K2, the Tibetan Plateau is often referred to as "the Roof of the World". The Tibetan Plateau contains the headwaters of the drainage basins of most of the streams in surrounding regions.