سنجش و ارزیابی الگوی گسترش فیزیکی شهر یزد

Introduction
Urban development in its evolutional procedure from the beginning has had a relatively balanced stream. But cultural, social and economic transformations of 19^th and 20^th centuries affected by modernism have caused rapid expansion of the cities and emergence of big cities. These changes have also modified physical-spatial organization and structure of the cities. This urban growth would have devious and infinite problems. One of the vital objects in the 21^st century in relation to the city constancy is urban growth form, i.e., compactness or dispersion.
     Yazd city is an example that has faced with rapid and dispersed growth. Despite of unity and compactness in the emerging phase, its sprout and organic growth is now suffering from an ill-fitting structure. Hence, it is necessary to analyze the spatial form of the city and population distribution and activity,, also its gathering and dispersion. According to the theoretical framework for analyzing the transformations of the physical dispersion pattern and the problem of the spatial form transformations in Yazd city during the recent years, two hypothesizes is suggested: 1) It has been assumed that Yazd city have had sprawl growth during 1966-2006. 2) It has been assumed that the spatial distribution of the population and their activity is not balanced in Yazd city. 3) It has also been assumed that the population and urban activity in Yazd City follows a dispersed pattern with no tendency in concentration. 
 
Methodology
This is an applied study on the basis of purpose and also a descriptive –analytical on the basis of nature and method as a kind of case-study. The required data for this study including the employment and population statistics of Yazd City based on administrative zonation of 2006. That was gathered by referring to the city hall of Yazd in the Statistics Center of Iran and the management organization of the Yazd Province.
     For examining the first hypothesis, Holdren Model has been employed. For examining the second hypothesis and evaluating the amount of balanced distribution of the population and employment in the city, Gini and Entropy indexes have also been used. In fact, the population and employment distribution could be balanced or unbalanced in different parts of the city.
     Dispersion and concentration of the population and activity have also been examined by the indexes of Moran, Geary and General G. Gathering and dispersion of the population and employment could have clustered, random or dispersed (checkered) patterns and concentration could be in the form of hot spot or cold spot.
 
Results and discussion
The results of examining the first hypothesis show that despite compact and regular development of Yazd City during 1966-1976, this city have had a sprawl development during 1966-1996. In general, the results showed that on the basis of Entropy index, there is some inequality in employment and population distribution in 9 zones of Yazd City. The Shannon entropy index for the area of the 9 zones of Yazd city in 2006 showed that it has a dispersed physical development. The results of analyzing the spatial distribution of population and employment using Gini method showed also that there are some inequalities and disagreements in distribution of these two parameters. In general, according to the calculations there are a few inequalities in the distribution of population and activity in Yazd city. Therefore, it can be said that the spatial distribution of the population and activity in Yazd city is relatively balanced. Thus, the first hypothesis is rejected.
     It seems noteworthy that if the urban parts had a cold spot of population and activity, then the existence of balance in population and employment distribution shows the sprawl. On the other hand, if the compression of the population and employment is high in the zones, the balanced distributions of population and employment shows a compact form for the city.
     By regarding the fact that the spatial distribution of population and activity in Yazd city is a little unbalanced and Yazd city has a cold spot of population and employment, we can conclude that Yazd City has a spatial sprawl form.
     The calculated Moran indices of employment and population of the both methods of measuring shows a random pattern which is more inclined to dispersion (checkered) than clustered pattern. The adjusted Geary index for population and employment of Yazd city was also calculated by using zero and one method. Both of them are cleared to random patterns and are inclined to the dispersion (checkered pattern). That has accordance with the results of Moran index. By regarding the calculations, Yazd city from the amount of population and activity gathering and dispersion point of view follows the pattern of random to disperse. The city from the concentration point of view has a cold spot of population and employment. The zones of Yazd city with low population and employment are concentrated near each others. Therefore, the second hypothesis is accepted.
 
Conclusion
Using these methods and the results we can conclude that the physical pattern of Yazd City is of sprawl pattern and we cannot see a compact and concentrated pattern. By regarding the necessity of directing the city towards more constancy, a necessity of change is felt to apply solutions and some suggestions for more compactness. Therefore, some necessary strategies for gaining a wise growth should be applied to monitor the physical development of Yazd City and promote a constant development and malting and also construct a healthy, well-proportioned, balanced and united city. These strategies are strengthening and producing urban spaces, government coordination in purchasing abandoned lands and properties, avoiding dispersed and sprawl constructions, organizing of land uses.