Over-concentration of population and activities, mainly in largest cities of the developing countries has attracted a large proportion of the development potentials of these countries into these cities. As a result, these cities have grown disproportionately larger than the second and the third cities of their countries. The phenomenon has been termed as "urban primacy" by Jefferson. Some developing countries, in order to combat the adverse effects of this phenomenon, have adopted certain policy measures. In Iran, in order to ameliorate the increasing problems of urbanization and the over-concentration of population and activities in Tehran, and to have a balanced countrywide regional development, industrial decentralization policies were devised and adopted. A battery of measures was also introduced to control development in the Tehran region. Several incentive and control measures were introduced to support the industrial decentralization program; chief among them was a decree, issued in 1967, banning the establishment of any large industrial establishment within 120-kilometer radius of Tehran City. In this paper the urban primacy in Iran during the four decades of 1956-1996 is examined. The main purpose of this paper is to find out if the adoption of decentralization policies during the said period has resulted in the reduction of over concentration of population and activities in Tehran and consequently in a reduction of its primacy level. After a brief introduction, the concept and theories of urban primacy is briefly reviewed. In the next section, methods of examining urban primacy has been explored and the following indicators, both for measuring urban concentration (primacy) and also de-concentration, have been selected to examine the urban primacy in Iran: Urban primacy index, two city primacy index, four city primacy index, Mehta's four city primacy index, Herfindahl concentration index, Moomaw and Alwosabi primacy index, Henderson de-concentration index, and entropy index.The results obtained from application of all six primacy indices indicate that the urban primacy was increased during the period 1956-1976, reaching to its peak in 1976, but has decreased from 1976-1996. Urban de-concentration indices also yield similar results and support the findings of the primacy indices. Although the indices indicate that urban primacy is decreasing since 1976 in the country, never the less urban primacy still exists in Iran, but its intensity has been reduced considerably. It was also found out that city size distribution in the country has been improved during the said period. The findings show that decentralization policies adopted since 1950s have been effective in reducing the urban primacy in Iran and has also contributed towards a better urban system in the country. The findings of the paper supports the prepositions made by Henderson that the governments can improve the city-size distribution of their countries by adopting certain decentralization policies.
)