According to the census taken in 1956, the total population of Iran was 18,944,821; it has increased since then at the rate of 2.4 to 2.5 per cent a year. Since Iran covers a vast territory of 628,000 square miles (1,648,000 sq. km), this means there is a fairly low numerical density: 18.5 persons per square mile or 12 to the sq. km. Less than a third of the population live in the cities, the remainder being peasants and part- or full nomads. The birth rate is very high (about 45 per thousand), while the mortality rate is about 20 per thousand. It is a surprisingly youthful population, and the first census showed that 49 per cent of the inhabitants were under 20 years of age, with only 4 per cent aged 60 and over. Movements of population in and out of the country (i.e. external migration) are not of great importance. But, on the other hand, the rural exodus, the drift from the country to the towns, presents a highly intractable problem; and the seasonal migrations of nomads are also considerable.

VARIATIONS IN DENSITY

The Iranian plateau, whose altitude fluctuates between 1,000 and 2,000 m above sea-level, is crossed by three imposing mountain ranges: The Alburz runs southward from the Caucasus, follows the curve of the Caspian Sea, and crosses Khurāsān to join the Hindu Kush and the Himalayas. The Zagros, on the west, runs south-eastwards from the Caucasus, extending as far as the Persian Gulf, and the third major complex of ranges running from north-west to south-east, crosses the eastern interior of Iran.