Morphological Analysis of Population Spatial Structure of Tehran Metropolitan Region (TMR)

Introduction“Form follows function” although is not a new concept, in last two decades gained more currency especially in spatial planning context that believed by investigating forms, function can somewhat be known. Analyzing spatial structure of regions as a means of spatial planning consists two main approaches; functional and morphological that investigate relational and nodal features of centers respectively. Spatial structure in metropolitan regions can be used in population and employment aspects that the first one represents settlement and the latter activity system of a region. In theoretical literature, these aspects are affected by three main factors, CBD, sub-centers and transportation networks. In the other handm, metropolitan region spatial structure is a fuzzy concept from mon-ocentric to completely polycentric, any region based on its social, economic, political and management system would be a degree of polycentrism. As spatial planning is an interdisciplinary subject, most of theories and methodologies are taken from different fields, so most of models in which used in this paper are economic based that combined by spatial aspects.
The aim of this study is that to analyze population spatial structure of population in Tehran Metropolitan Region (TMR) in a morphological context. So it can be divide to three question: what is the relation between population distribution and distance to CBD? Secondly, how much population density in TMR been affected by transportation network? And the last, what are TMR sub-centers and is there any relation between them and population density?
MethodologyMain approach of this research is morphological that mostly refers to plurality of centers in a given territory. Ass the main object of this study is assessing the influence of some factors on population distribution, we used various type of regression functions. The most important data for these methods that commonly used is population and employment density and transportation networks that both of them are gained from Statistical Center of Iran (SCI) corrected by authors. To evaluate relation between CBD and population density, different forms of monocentric function adopted that the most useful and commonly used forms are linear, gravitational, exponential and logarithmic. In terms of transportation networks (highway and freeways) is used several forms of univariate regression function to assess relation of population density and distance to nearest network. Third part of this study is evaluation the influence of subcenters on population density that is more arguable because of the variety of methods on subcenter identification that most of them have a kind of arbitrary. However, a combination of adopted models are used that consists, threshold method, density and proportional based method, parametric model, GWR and ESDA. Then in a multivariate nonlinear function relation between population density and distance to nearest subcenter. At the end a linear integrated model used to ass the population density changes based on distance to CBD, transportation network and subcenters simultaneously. In all cases used OLS technique to ass the models.
Results and discussionAs said, this study was conducted on the Tehran Metropolitan Region (TMR) where the most important and populous region in Iran. TMR was encompassed Tehran province but by the parliamentary approval (2010) politically divided into two province (Tehran and Alborz). Tehran is the seat of the Tehran province and Alborz centered in Karaj. Tehran city is been the capital of Iran from 1776 up to now and population is increased from 15000 people to 8154051 in 2011. In this period Tehran has been became to a great metropolitan region that according to last census (2011) by 18000 square kilometers area (1.1 % of the total area of Iran) and 14 million population (19 % of whole population of Iran) product more than 30 % of total gross product. TMR as mentioned, encompass 2 province (ostan), 14 county (shahrestan), 54 city and 87 rural district (Dehestan) in total 141 administrative border. As table 1 and figure 1 show, population decentralization is started from 1976-86 that refers to 1979 revolution happening. It should be noted that incremental rate of population proportion of the rest of TMR doesn’t mean that these inhabits come from Tehran city and even attracted from other parts of country. Decentralization process in Iran absolutely is different from western countries. In other words, population decentralization in most of western metropolitan regions refers to a situation that population from center go to periphery but in Iran mostly the rest of Metropolitan is the destination of migrants of non-center inhabits.
The results of monocentric model who assess relation between population density and CBD, shoes no significant relation (R2=0.1) and means that CBD cannot explain the population density variation while OLS results of road based models shows not considerably significant but powerful relation between population density and distance to highway and freeway compared to CBD variable. All of methods mentioned before is used to identify subcenters and the final output confirmed the existence of subcenters in TMR and presented six of them; Karaj, Eslamshahr, Baghershahr, Nasimshahr, Varamin and Rey. In the next step OLS results of regression model demonstrated a high goodness of fit value (R2=0.5) that confirmed the hypothesis of slight polycentric structure of population distribution. And finally the results of integrated model who was testing the importance degree of triple variables (CBD, subcenter and transportation network) on population density surprisingly demonstrated that road is most important factor, subcenter and CBD are in lower level of significance, that t-value of OLS results is -5.65, -1.18 and 0.45 respectively.
ConclusionThis research aims to describe and analyze the population spatial structure of TMR. The results showed significant influence of transportation network and subcenters and on the other hand inconsiderable role of CBD on population distribution over TMR territory. Therefore, the empirical evidence obtained for the case TMR allow us to state that: monocentric model cannot explain the dynamism of TMR population structure, whatever it doesn’t mean that TMR is polycentric but that results though not significant, showed a degree of polycentrism and network based structure.