تحلیل فضایی فرم شهر بابل براساس تراکم ساختمانی

Introduction
Urban form is defined as the spatial distribution pattern of human activities at a certain point in time. It is made up of the visible elements and components of cities and consists of natural and artificial elements as the spatial crystallization of the community activities. Awareness of the spatial form and the shape of the city can be one of the important factors influencing the success of urban planners and managers. The importance of this issue has led to the use of various methods for measuring urban form in recent years to determine the distribution of compression. In Iran, in urban development plans we have used building density as a means of curbing urban development and spatial equilibrium, but in many cases, the discussion of density and analysis remains only in the scope of the plan; because today in the cities in north of Iran there are cases of irregular urban growth and without planning. This can bring heavy expenses for the city managers. Knowing the density category and the analysis of cities with appropriate indicators are considered as one of the most important factors in achieving a sustainable form of city. For this reason, this study seeks to make a scientific analysis of these issues. We are to examine the physical form of Babol city as one of the northern cities of Iran that has grown significantly in recent years.
In general, the city forms can be classified into three groups: Density, diversity and pattern of spatial structure. The spatial structure of cities may be defined in different ways: It is possible to indicate monocentric land use versus polycentric land use, centralized patterns versus decentralized patterns and continuous development against discontinuous development. The “building density" is equal to the ratio of the underlying area to the area of land. The effects of increase in the density are considered on the urban form in the spatial structure, physical system, urban landscape, connections of the walls, and building collation. Density is an important indicator to declare sustainable urban forms that its advantages can be divided into three categories of economic, environmental and social aspects.
Methodology
Based on the nature of this topic and the objectives of the study, the dominant approach in this study is descriptive - analytical. The statistical population is 22 districts of Babol city based on the new division of the municipality in 2013. In this study, building density was calculated based on statistical blocks. Information needed to calculate the building density is achieved by dividing the total area of residential blocks infrastructure building density into the area of each block according to the Population and Housing Census in 2011. To display the amount of building density, we used the contour lines for the spatial analysis method. For measurement, we have used the spatial analysis models like Moran coefficients, analysis of Hot Spots Analysis, weight regression and Pearson correlation.
Results and discussion
Analysis of the relationship between building density and population indicate that in the central and northeastern part of Babol (regions 5, 15, 17 and 18), the population has more correlation with building density. This determines the building density in these areas. The analysis of population impact on building density show that the northern part of Babol (regions 1, 2, 18, 19, 20, 21 and 22) population density has a greater effect on building density. In other words, in the mentioned areas, the effect of population density on building density is higher than the other areas. The population density is an important factor in the building density. Analysis of hot spots suggests that the city of Babol has two cluster densities in six neighborhoods including districts of 2, 3, 5, 6, 14 and 16. Increase in the number of density clusters in the western part of the city, especially in the northwest, has led to an increase in construction in this part of the city. This is while the central and southern parts of the city are low in building density. The relationship between building density and distance from the center of the city, with coefficient (0.49), is a significant and inverse relationship. There is also a significant relationship between building density and population and residential density.
Conclusion
In the current century, the issues such as population increase, the need to settle in cities, population distribution, renovation of urban development, and public demand to live or work in a certain place are among the factors encouraging increased urban building density. Weakness of planning system the policy to increase building density not based on the reception capacities of the urban system based on demand and without limitations. The self-sufficiency policies of the municipalities led to building density as a key factor in housing and urban development policies. Obviously, the principle of construction congestion as an important tool to control urban planning and urban development has many negative consequences in Babol city. Inability to provide welfare and urban services as well as the inability of infrastructure to provide services to the growing population are the major  threats to a healthy urban life due to increased building density in places with no capacity in the area with residential neighborhoods.