بررسی نحوۀ گسترش فیزیکی شهر ارومیه با استفاده از مدل های کمی

Extended abstract                                                                                                                
Introduction
One of the most important and dominant issues discussed on the international environmental problems is the concept of "sustainable development" and the relationship between urban form and sustainability. This has posed more discussions like the way in which the cities should be developed in the future and the effects their form can have on resource depletion and rational use of environmental resources. In order to achieve the sustainable urban form, different models and approaches, mostly two opposite approaches were introduced: "Compact city" and "Urban Sprawl".
Urban sprawl was a reaction to industrial city which is normally conceived as a combination of low- density, scattered and strip development patterns. Researchers have summarized the various definitions of urban sprawl in the planning literature to create a working definition of the concept as: ‘…unplanned, uncontrolled and uncoordinated single use development that does not provide a functional mix of uses and/or is not functionally related to surrounding land uses. This is variously appeared as low-density, ribbon or strip, scattered, leapfrog, or isolated development.
Different impacts of urban sprawl, mostly negative ones have come under increased criticisms in the recent years. This change has occurred in conjunction with an increasing awareness of human impact on the environment and the emergence of ‘sustainability’ as a concept of international significance. The ‘Sustainable development’ has become most popularly understood from its definition in the report by the Brundtland Commission as ‘development which meets the needs of the present without compromising the ability of the future generations to meet their own needs and aspirations’. Urban sustainability and sustainable urban form was introduced mostly through ‘compact city’ theory. But at the end and according to different academic conflictions, different considerations of compact city should be adapted to local and environmental conditions of different regions and countries.
In our recent conditions in Iran, we should respect to our resources and try to use them in the most logic way. Unsuitable growth, horizontal development, and urban sprawl have occurred even in the places the land is a critical issue which causes destruction and loss of farmlands around the cities and other disadvantages. These issues emphasize on the importance of logical and conscious development of the cities.
The main purpose of this research is to examine the physical development in city of Urmia in the recent three decades. It tries to reach this point of view whether if the existing development process leads to sustainability or it moves towards unsustainability. The importance of this issue is because of the existence of the valuable farmlands around the city of Urmia and agricultural role of the city in the different plans.
 
 
Methodology
Historical, explanation- analysis method, experimental and case study are the approaches used in this research. Necessary data like population, city area, density, urban land use and etc. from different sources have been gathered and studied by different methods and quantitative models of urban physical development. Holdern and Shanon Antropy models are used to analyze the results, in the next stage.
 
Results and discussion
Holdern, Shanon Antropy and many other quantitative models are used to examine the process of physical development of urban areas. These models can estimate the amount of urban development according to population needs and the amount of urban sprawl.
According to different analyses, the total urban area of 1400 hectares of Urmia City in the 1976 has exceeded to more than 8578 hectares in 2006. This is because of the urban growth especially in the suburbs. This amount of growth does not fit the population growth in the same time. In the last three decades urban population growth was nearly 3.5 % while growth urban area was nearly 6 %. The results show that the growth process in city of Urmia in the recent 3 decades has moved toward the unsustainability and is greater than population needs. According to Holdern Model analysis, it is estimated that 69.9% of urban growth is because of population growth and 30.1% related to sprawl development of the city which causes destruction of rich farmlands. Therefore, appropriate decisions must be made in order to cease this process and move toward urban integration and compactness.
 
Conclusion
The results of this research indicate that the use of compact city form instead of sprawl spread can increase its sustainability. Land use Analysis of the Urmia City shows that 2251.8 hectare or 26.2% of whole city is barren. By this potential, urban management can guide the physical growth of the city and prevent its horizontal growth. Shanon Antropy coefficient analysis on city of Urmia at this regard approves the sprawl growth form. Therefore, with emphasis on this technique for verification of the sprawl growth, mono or multi forms of the city can increase error coefficient; for computing exact results on spatial structure form of the city needs other coefficients like Moran and Geary.
The results of the research indicates that if the current process of urban growth continues in Urmia in the future, the most valuable farmlands will be destroyed and the attraction of suburbs will result in the ruin of city centers. Thus, different decisions should be made to reduce unsustainability process.