عوامل تأثیرگذار بر تحولات ساختار فضایی-کالبدی کلانشهرها (مطالعه موردی: کلانشهر تبریز)

Extended Abstract
Introduction
The spatial organization of the city is the result of all human, natural and man-made forces, which have both objective and mental manifestations. Therefore, the way each city grows is influenced by many factors such as its natural limitations and facilities, the policies of planners and how land is used, and many other factors. In this regard, nowadays, knowledge of the spatial structure and shape of the city and the factors influencing their changes can be one of the important influencing factors in the success rate of urban planners and practitioners and can greatly help to improve urban environments. For this purpose, it is necessary to examine the pattern and physical-spatial structure of the city and the reasons that have governed its spatial expansion in different periods in order to prevent physical, social, environmental and economic problems and inadequacies in cities and control its expansion. Considering the importance of identifying the factors affecting the physical-spatial changes of cities, the present research was written with the aim of identifying the factors affecting the changes in the physical-spatial structure of Tabriz metropolis. The metropolis of Tabriz, as the largest city in the northwestern region of Iran, has witnessed extensive changes in its body and population from 1966 to 2016. If the population of the city has increased almost 6 times (from 289,996 people to 1,773,033 people) and the physical development of the city has increased about 16 times (from 1170 hectares to 19000 hectares). Along with this expansion in area and population, the body of the city has also undergone extensive changes, including the formation of various towers and skyscrapers in different areas of the city, as well as the settlement of more than 450 thousand people in informal settings (especially in the northern part of the city). Cited. On the other hand, with the increase in population, various issues such as increased traffic and air pollution have appeared, especially in the central part of the city, and we have witnessed the formation of new functional cores, especially service and economic ones, at different levels of the city. In this regard, it can be said that many functions that were often developed in the central areas of the city at different stages, have expanded to different levels with the prosperity of urban lands and the service sector. Therefore, identifying the influencing factors on the structural-spatial developments of the city can provide the foundations for the sustainable development of the city.
 
Methodology
Considering that the present research seeks to identify the influencing factors on the changes in the physical-spatial structure of Tabriz metropolis, therefore, the research method is practical in terms of purpose and analytical-developmental in nature. For this purpose, first through documentary studies, indicators related to spatial-physical structure changes were extracted, and then, through questioning of the sample size, the influence of each of the indicators on spatial-physical structure changes of Tabriz metropolis was determined. Also, in order to analyze data and information, structural equation modeling method was used in AMOS software. It should be noted that the statistical population of the research included academic elites and city managers of Tabriz, and due to the unknown size of the statistical population, Cohen's formula was used at the 95% confidence level to determine the sample size.
 
Results and Discussion
The findings of the research show that the most important variables affecting the spatial-physical structure of Tabriz metropolis are technical-technological, economic, physical-environmental, managerial, and social-cultural, respectively, and their influence is 0.75, 0.71, 0.66, 0.58 and 0.52 based on the structural model. Also, among the sub-variables, the most influential on the changes in the physical-spatial structure of Tabriz metropolis are related to information and communication technology variables, the difference in the economic value of housing and urban land, the expansion of access (streets and passages), urban services and smart citizens, and the expansion of centers and cores. It has been a new business in the city.
 
Conclusion
In the metropolis of Tabriz, during different periods, especially after the land reforms, we have witnessed extensive changes in the spatial structure of the city. The expansion of the marginal areas, the formation of the new cities of Sahand and Shahriar, the creation of new commercial centers and residential areas, etc. are some of the developments in recent years. The changes made in some cases are evaluated positively and in some cases negatively. For example, the formation of new commercial and demographic cores (in line with the proper distribution of population and functions) is one of the positive points, and the wear and tear of some structures and infrastructures are considered negative points. It can also be said that in the metropolis of Tabriz, despite the changes in the physical-spatial structure based on influencing factors such as society, economy and the existing political and administrative system, spatial balance has not been formed and spatial inequality and polarization in the spatial structure of the city (new Tabriz in the east and old Tabriz in the center and west). For this purpose, the present research was written with the aim of identifying the influencing factors on the changes in the physical-spatial structure of Tabriz metropolis, so that by identifying these factors, preparations for development and proper planning can be made. According to the obtained results, it can be said that the most important factors affecting the spatial-physical structure of Tabriz metropolis are: technical-technological factors, economic factors, physical-environmental factors, managerial factors and socio-cultural factors. Also, in different dimensions, the impact of information and communication technology and the formation of smart urban services, the formation of commercial cores and their distribution in different levels of the city, increasing the accessibility and suitability of surrounding lands for construction, urban plans and laws, and the increase in population and intra-city relocations can be seen in the developments spatial-physical structure of the city pointed out. Therefore, by identifying the influencing factors on the spatial developments of Tabriz metropolis, plans and planning should be prepared with the approach of spatial justice in order to prevent the growth and expansion of the city and the destruction of all kinds of resources in addition to achieving spatial balance in access to all kinds of resources and facilities.