An Analysis on Physical Extension Factors and Spiral Pattern ofTabas City After Earth Quake by Holdrem Entropy Model

During the last decades, Iranian cities like many other cities in the third world have been undergone remarkable changes. One of these changes is rapid population growth and urban spiral expansion inmost of Iran's cities due to the lack of program for proper use and with a scientific basis of urban lands.Tabas city like many other cities of Iran has not been immuned from these changes and its population has tripled during the last 30 years, which this increasing population growth, has caused uncontrolled expansion of the city, so that, this city with physical expansion of more than 6 times during this period has caused some problems with undesirable results including increasing the price of land and house, shortage of infrastructural facilities, destruction of agricultural lands located around the city. Now, in order to balance these civil inadequacies, this paper analyzes the physical extension of Tabas city after the earth quake and the effective factors on it and has investigated the probable guidelines and methods for removing and balancing this process. The method applied in this research, was descriptive - analytics method which for data analyzing, Holdern models, location coefficient and increasing employment and population model have been used. The results show that %55 of physical growth of the city in the years between 1976 up to 2006 has been occurred due to the population growth and %45 related to horizontal and spiral growth of the city, while based on the calculations made by the writers, the present limit of the city with inner city expansion will be responsive to the needs of city population up to the next 19 years. In analyzing the effective factors on physical expansion of the city, the obtained results of the research confirms that natural elements such as smooth topography, proper slop of lands in north part of city, social factors of population growth and especially rural- urban migrations and economical factors especially the existence of large coal mines, merging large village of Dihshak to Tabas city are considered as one of the main factors. Among the findings which help to stop the uncontrolled physical expansion of the city, we can refer to inner texture of city expansion, development the culture of vertical expansion of the city and finally providing the welfare facilities in the cities.