The present Iranian state covers an area of some 628,000 square miles (1,648,000 sq. km) and extends between latitude 25° and 40° N., and longitude 44° and 63° E. More than six times the size of Great Britain and approximately three times the size of France, which is the largest country in Western Europe, Iran has a frontier that has been estimated at 2,750 miles in total length, of which over half is sea coast, with 400 miles lying along the southern Caspian shore, and the remainder (1,100 miles) comprising the northern parts of the Gulf of Oman and Persian Gulf. From the extreme north-west to south-east—at approximately the frontier with Turkey and the U.S.S.R., close to Mt Ararat, as far as the Baluchistan border just east of Chāhbahār—is a total distance of 1,450 miles; whilst an opposite diagonal, so to speak, from Bushire (Būshahr) to the Soviet frontier north-east of Mashhad, would measure 830 miles.

Physically, Iran consists of a complex of mountain chains enclosing a series of interior basins that lie at altitudes of 1,000 to 4,000 ft above sea-level. These mountain ranges rise steeply from sea-level on the north and on the south, and equally abruptly from the very flat and extremely low-lying plain of Mesopotamia to the west. Eastward, and also in the extreme north-west, the highlands extend beyond Iran in the form of largely continuous and uninterrupted features: in the first area they are prolonged as the massifs of Afghanistan and Baluchistan (West Pakistan), and in the north-west as the plate uplands of Russian Azerbaijan and eastern Asia Minor.