a. mojtahedzadeh

Improper allocation of resources and facilities to privileged areas and deprivation of other areas has led to inequalities in economic development.. The purpose of this study is to determine the Semnan urban ergion using the method of measuring flows (bottom to top).

From the city center of Semnan, a radius of 20 and 50 km was hit in the GIS environment. Semnan city was selected as the main city and the cities of Dargezin, Sorkheh, Shahmirzad and Mahdishahr were selected as the surrounding cities.To determine the urban region, the amount of population moved between the two cities and the amount of goods moved should be calculated and the final score of each city should be calculated by being in the relevant formulas.

According to the calculations, the final score index (iT) of Sorkheh and Dargezin cities were 11.72 and 18.83 with moderate correlation, Mahdishahr with 28.54 had high correlation and Shahmirzad with 38.5 had very high correlation with Semnan city. The boundaries of Semnan urban region can be determined including the two parts of the center (Semnan city) and its surrounding territory (Mahdishahr and Sorkheh cities).

The spatial equilibrium situation of Semnan urban system from single-center mode in recent decades with increasing number of peripheral cities and regional divergence of population, has tended to multi-center development with a balanced speed, but still far from creating full regional interaction The creation of Semnan urban area has accelerated this process.