Iran is situated in South-West Asia and has a surface area of 1,648,000 km2 (636’000 sq mi). It lies on an elevated plateau between the Caspian Sea to the North and the Persian Gulf to the South. The central plateau is surrounded by the mountain ranges of Alborz and Zagros. The dryness of the terrain at the foot of the mountains is offset by oasis after oasis of cultivated land, where grain, barley, cotton, and fruit orchards have formed the basis for the growth of towns and villages. Only the Caspian and Azerbaijan provinces have sufficient annual rainfall to ensure abundant greenery and luxuriant vegetation.