Mustang, the second least populated district of Nepal, is flanked by the Nepalese districts of Manang, the least populated, to the east and Dolpa, the third least populated, to the west. The Tibetan frontier stretches north from Mustang's borders. Mustang is divided into two sub-regions, Lower and Upper. This is a high-altitude trans-Himalayan region spread over 3,640 square kilometres in area barely north of the main Himalayan mountain range. Geographically this cold high-altitude steppe is a part of the Tibetan highlands. This boot-shaped piece of land thrusts north into western Tibet is caught in the rain shadow of Dhaulagiri to the south and west and the Annapurna Massif to the north and east.