Determining the Urban Region Using the Gravity Method (Measurement of Flows and Distance from the Center) and Resilience Analysis of Urban Areas (Case Study: Semnan Urban Region)

The development and expansion of urbanization in the twentieth century has led to the formation of different spatial organizations in urban and regional patterns. Semnan city with a strategic position in the country's communication network and proximity to the capital and industrial, mining and agricultural potentials due to changes and implementation of political divisions in the last decade and the promotion of small towns around Semnan to the city without paying attention to interconnections and demarcations performance encountered. Existence of flows of goods, manpower, and interurban and peripheral services represents a range of activities that cannot be stopped within local boundaries. This study has used the gravity method (measurement of flows and distance from the center) to determine the boundaries of Semnan urban area and its purpose is to determine the boundaries of Semnan urban area based on functional relationships. From the city center of Semnan, a radius of 20 and 50 km was hit in GIS, the city of Semnan was selected as the main city and the cities of Dargzin, Sorkheh, Shahmirzad and Mahdishahr were selected as the surrounding cities. In the flow measurement method, the amount of population displaced between the two cities and the amount of goods displaced were calculated and the final score (iT) of each city was calculated by including the relevant formulas. According to calculations, the cities of Sorkheh and Dargzin are with moderate correlation, Mahdishahr with high correlation and Shahmirzad with very high correlation with Semnan. In the method of distance from the center to determine the boundaries of Semnan urban area, a suitable distance for the maximum distance that Semnan city can affect the surrounding urban areas while maintaining the nature of its city-regions (the easiest time to reach the main city) is specified. Besides, cities that have the desired level of points are located in the urban area using this method. From the overlap of the maps obtained from the methods of measuring flows and distance from the center in GIS, Semnan urban area was determined based on statistical functional relationships and the area of Semnan urban area consisting of Semnan, Dargzin, Sorkheh, Shahmirzad and Mahdishahr cities. The total resilience level in Semnan region is equal to 3.21, lower than the average of 3.5. As it was said before, only the social and cultural dimension is resilient and in terms of other dimensions, especially the economic and institutional management dimensions, resilience is at a very low level.