بررسي تاثير سياستهاي فضايي بر ساختار فضايي شهري با تاكيد بر تراكم ساختماني مطالعه موردي: تهران

Investigating the Impact of Spatial Policies on Urban Spatial Structure with Emphasis on Building Density (A Case Study of Tehran)

ساختار فضايي شهر ميتواند بر ابعاد مختلف توسعه شهري تاثير جدي برجاي گذارد، اين مسيله با توجه به مشكلات محيطي مانند آلودگي هوا، ترافيك و تغيير كاربري اراضي به ويژه در كشورهاي در حال توسعه مثل ايران، توجه برنامهريزان شهري را به خود جلب كرده است. از اين رو هدف اين مقاله بررسي ساختار فضايي تحتتاثير سياستهاي فضايي مربوط به تراكم ساختماني در شهر تهران به عنوان يكي از شهرهاي جهان سوم است. روش تحقيق توصيفي - تحليلي است و با بهرهگيري از تكنيكهاي آنتروپي شانون، تراكم، آزمون T و مدل hot- spot به تحليل چگونگي گسترش كالبدي- فضايي شهر تهران پرداخته شده است. نتايج حاصل از مدل آنتروپي شانون و hot- spot كه در طي سالهاي58- 5731 انجام شده، نشان ميدهد كه شهر تهران داراي الگوي رشد پراكنده است. همچنين ساختار فضايي شهر تهران در هشت جهت جغرافيايي نشان ميدهد كه با توجه به توزيع تراكم ساختماني و جمعيت، ساختار فضايي شهر تهران فاقد بخش مركزي قوي ميباشد؛ اما بعضي از شواهد حاكي از حركت به سمت فشردگي نامحسوس در سالهاي اخير است. الگو پراكنده ميتواند تاثيرات منفي زيادي در بخشهاي مختلف اقتصادي _ اجتماعي و زيستمحيطي به بار آورد، بنابراين ابعاد فضايي سياستها در برنامهريزي تراكم ساختماني بايد مورد توجه قرار گيرد.

As the greatest invention of human being as well as a living organ, city exceeds beyond a physical mechanism or a built structure. The emergence of industrial revolution has brought about widespread changes in the distribution of population and spatial structure of cities. Spatial structure of cities as one of the important urban sub-systems seriously affects the different aspects of urban development. In developing countries such as Iran, the changes and problems resulting from unfounded decisions as to the spatial policies (i.e. policies leading to the distribution of activity and population in geographical sphere such as density) transformed the spatial structures. The inefficiency of control mechanisms, lack of congruity between objectives of plans with existing realities, inflexibility of plans, weakness of local governors in provision of financial costs, widespread land use changes and above all density sale has introduced incorrect spatial policies culminating in mushroom growth of cities and a disturbance in spatial organization. Thus, this paper aims to investigate the spatial structure in terms of spatial policies in relation to building density in Tehran as one of cities in a developing country. The research methodology is descriptive-analytical using Shannon entropy, density, T test, Hot Spot techniques in analyzing the trend of physical-spatial expansion of the city. Moreover, Arc GIS and Excel were used for data processing. The result from Shannon entropy and hot-spot revealed that the city experienced sprawl growth pattern from 1997 to 2007 and the spatial structure of the city in eight geographical directions showed that the city lacks a strong central part regarding the distribution of building density and population. By reviewing the spatial policies of density of Tehran city, it becomes clear that spatial policies have been made on the base of financial issues rather than spatial aspects especially after cut of state funding aids to municipalities in 1386(2008) which encouraged the lease of density and consequently spatial disturbance in the city structure. Evidence shows that the city experienced compact growth on a limited scale. Therefore, the change profile of building density from 1375 to 1385(1997 to 2007) indicates that there is a higher density from 1375 onwards. As mentioned, such a change is inspiring in that the central parts have more population and higher building density. The result from T test showed that the central zones are increasing their building density, too. There is, however, not only inconsiderable change in building density and the extent of activity in central and peripheral zones from 1382 onwards but also a dispersed pattern. The important point is that however improper density lease may seem but this research emphasizes the quality of spatial distribution for density. Overall, Tehranʹs spatial structure has no proper order and its city pattern follows a sprawl expansion. This pattern can have negative impacts on the city such as air pollution, travel time etc. and impose extra costs on urban authorities and the citizens. Therefore consideration of spatial aspects of policies in planning the building density is a main priority.