عنوان مقاله [English]
In changes made in urban networks relying on new theories, the made researches cannot describe any more the structure and function of urban networks of state completely, but the need of using integrated and interactive approach based on networks felt for assessing the situation of this system. Increasing the number of metropolises, is an expression of extraordinary concentration of population in certain regions of developing countries and these changes are dependent on a new logic of development-the logic in which the new image of regions is primarily a mix of links and nodes ,and has the more emphasis on integrated look to centers and regions. Each center in urban network has different situation, status, and character according to degree, type, composition, and opportunity in relation to others.
In this study, we will try to consider both physical and interactive approach simultaneously, and study about different views of urban network aim to draw out different spatial representations of under-changing urban network of Tehran metropolitan region based on three views of node, density, and accessibility. In this regard, we will study about how is changing process of functional and morphological systems of urban network of Tehran metropolitan region, and the relationship between them in three time periods.
Essentially, the morphological approach shows size and distribution of urban centers of country, and considers the more balanced distribution as equal with network model and multi-centralization. The morphological approach focuses mainly on the fact that the centers should be, physically separated from each other through open spaces distinctly. At the same time, the distances should be such that allow region to be considered as a regional identity through interaction and the lease proximity. From morphological point of view, the centers should not be superior to each other in terms of importance; therefore, chronological ranking between cities is normally evaluated according to population of them. Functional (communicational) dimension imply functional links between residences which consider mutual and multi -lateral communication as equal with more functional network model. From functional point of view, centrality and centralism should not be formed in interactions between urban centers of region.
Therefore, chronological ranking of cities is measured with relation scale, which often done in the stream of people, goods, or information using network analysis. Functional look with inclusion of morphological dimension insists on interaction in distribution of functional relation. Such a balance show equality of distribution of internal flows of a system which is not driven to one center, but it is bilateral and crossover. Recently, main contribution of functional approach adds another dimension which is network congestion. The rate of network congestion shows the extent of centers dependency in one center functionally, and could be conceptualizes as the ratio of actual relations between centers to sum of their potential relation.
functional analysis: The outlines degree of urban system has been measured based on network analysis, and ranking point of outline has been achieved using measured value. Studies indicate that Tehran city ranked first outline in 2001 and play athlete role in the region, while the cities of next rank deployed Western and Southern parts of under-study region which shows the dominant situation of metropolis of Tehran, and its dominant relation with Western part of region.
The results of analysis during 2006 shows that the degree of existing urban network outline has been changed compared to previous period and the differences of outlines degree decreased , and intensity of concentration of urban network has been reduce totally. Nonetheless, during this period to urban points of Tehran and Karaj are still known as dominant points in region. It can be said in spite that the activity system of region is developing between urban points, total collection has been more dependent on Tehran. Surveying the results of urban network analysis in metropolis region of Tehran on 2011, shows that urban network communication in Eastern part of limited region could have better function in relation to previous periods and increase its functional role in urban structure. However, strong communication between Central and Western regions has standard function.
The functional ranking of cities in metropolitan region of Tehran has been changed in each period compared to previous period and the differences between points has been reduced with regard to outline power, while three top cities is still fixed. There are meaningful differences between two top cities, that is Tehran and Karaj, compared to other points. However, changes of outline power between other cities indicates changes made in network and also strength of achieving urban points of the region.
morphological analysis: Surveying the morphological pattern of urban system of metropolitan region of Tehran in 2001 is expression of a relatively linear structure drawn from West to Center part and extended from Center to East and South parts of collection. According to analyses stated, the centrality of this structure is Tehran, Where all main communication leads to. Changes of pattern of urban system during 2006 have been emerged in the form of previous period development. In fact the structure of pattern of this period is the same as previous period structure which has been developed in Eastern, South, and Western parts. Of course this development is in the form of creation the chronological relationship from small centers of marginal zone of metropolitan region of Tehran to urban adjacent points. The Eastern parts of the limited region have been more than other parts in development of urban system.
Surveying the pattern of urban system of metropolitan region of Tehran in 2011 shows that the urban system of the region has been undergone changes compared to previous period ,and the old pattern is developing to Star Pattern such that Tehran city direct all the relations of region toward itself as center of this pattern as well as the prominence of ridge of Star pattern toward the West indicates more importance and influence of this part of region in forming the pattern of urban system of region.
Adaptive analysis of urban network function on morphology: In surveying and local analyzing of the extent of conformity of functional analysis with urban network pattern, it can be seen that in 2001, there is much conformity between these two indices in central and south parts. However, the western parts of the region has also compliance to a large extent, while the eastern parts of region has not much local correlation between these two indices. local analyze of the situation of functional system and pattern of urban network in metropolitan region of Tehran in 2006 shows that functional field and the role of urban point in analyzing the functional system in this period has been increased compared to previous period and the network congestion in region has been provided more expand surface in this period. From this, it can be concluded that the urban relationship has been increased during this period, and the system of urban network has been led to a greater integration. On the other hand, surveying the pattern of urban network during this period shows that the urban points developing the pattern of urban network have been increased and the indices of pattern of urban network have been developed. With regard to relative local conformity of these tow analyze, it can be said that the results of these two analyze during this period have more local dependency compared to previous period.
In local surveying of the situation of functional system and the pattern of urban network of metropolitan region of Tehran in 2011 it can be seen that there is relative conformity between these two variables with regard to local situation. However, The central and medial parts of metropolitan region has more network congestion which indicates the functional role of this region in metropolitan region, whereas the pattern of urban network un this period also insists on medial part; such that the metropolis of Tehran, as the center of Star pattern, has important role and station in the pattern of urban network. On the other hand, developed indices of the manes of star pattern govern on the urban network of are also located in relation with streams arising from network analysis , such that it can be said the functional system governing the region is in compliance with pattern of urban network. Of course it is worth noting that the degree of conformity in western regions is more than eastern one in terms of location.
Examining the regression relationship indicates that there is a relative relation between regional functional system and the pattern of urban network of metropolitan region of Tehran during 2001 and 2006. This indicates he relative dependency of these two indices. In fact it can be said that, this dependency in medial parts is more than other parts according to local analysis, because marginal parts of pattern of urban network has little relationship with medial parts according to network analysis and this reduces the dependency coefficient, Such that the farther urban points has more relationship with urban points around itself than metropolis of Tehran (as the central of Tehran metropolitan region).
Surveying the regression relationship during the period of 2011 shows that this coefficient has been decreased compared to last period; however, this amount which is equal to 0.635 has been more than first period (2001). This means that a casual relation can be visualized between these two variables in under-examine region totally; because, the regression coefficient higher than 0.6 indicates the casual relation between tow variables. It can be said that the functional system and the pattern of urban network in Tehran metropolitan region is fit and connected together in the course of this developed period. This means that the morphological characteristic of urban network of metropolitan region of Tehran in this period has been shaped based on functional characteristics and vice versa.
The results and surveys showed that, during the examined periods, the changes process of functional system of urban network of metropolitan region of Tehran tends from functional concentration in a dominant point to network and functional distribution pattern.
Aslo, the morphological pattern of network of metropolitan region of Tehran during the examined periods is developing with cluster patterns through providing relationship in new urban points, and finally the existence of meaningful relationship between functional system and morphological system of network of metropolitan region of Tehran proved.
It is suggested that the relationship between fashion pattern of urban network and activity system and spatial pattern be noted in regional programming ,such as region logistics which surveys and studies about the metropolitan region of Tehran. On the other hand, with regard to this relationship in the region, another suggestion is developing regional balance in terms of urban network using residence system and activity system. Such that the regional balances in different fields based on this relation can be regulated and programmed for the region according to this relation. This research could explain the relationship between two main components of urban network of metropolitan region, but in order to assess the raised relationship, indices and other factors have been considered isolated which can be considered as new issues to achieve even more precise results in future researches.