Analysis On The Evolution Of Urban Spatial Forms In The Main Urban Area Of Leshan City

In 2016,the "Chengdu-Chongqing Urban Agglomeration Development Plan" proposed to build Leshan into a central city in the Chengdu Plain and a spatial node city radiating southward from the Baocheng-Chengdu Development Axis.This requires Leshan to comprehensively upgrade its urban energy level,coordinate its urban functions,expand its new development space,and play a radiation-driven role in surrounding areas,thus can be the ture “bridgehead” of the southward opening of the Chengdu Plain.These requirements not only promote the development of Leshan city,but also put forward higher standards for the spatial layout of Leshan city.Therefore,the analysis on the evolution of Leshan city form has important theoretical and practical significance.In this thesis,the urban built-up area of Leshan city is taken as the research object,and the urban built-up area outlines of Leshan city in 2002,2007,2012 and 2017 are extracted by using GIS spatial analysis technology.The area and perimeter of built-up area in different periods are counted.Observing the change of speed and intensity,compactness and fractal dimension of urban space expansion in different stages,and combining the equal fan analysis method and the gravity center transfer method to summarize the evolution characteristics and rules of the outer space form of the urban built-up area in Leshan City.Then the evolution process and internal mechanism of the inner space structure of the city are analyzed by the circle analysis method.Combined with SPSS software,the factors affecting the evolution of urban spatial form are analyzed.Finally,on the basis of summarizing the achievements of urban construction,this thesis analyses the problems existing in the development of urban spatial form,and puts forward corresponding development proposals in order to better guide the construction and development of urban spatial form in the main urban area.The main conclusions are as follows:(1)From 2002 to 2017,the area of urban built-up areas in Leshan City's main urban area increased continuously,and the external spatial form of the city changed significantly.The urban expansion of the main urban area has gone through a process from slow to intense to steady expansion.The compactness index of urban built-up areas is generally low and showing a downward trend.The fractal dimension of urban built-up areas increased from 1.44 in 2002 to 1.89 in 2017,which indicates that the shape and boundary line of urban built-up areas are more complex.The main direction of urban spatial expansion has changed from initial NWW to SW-SWW,and then to final NW-SW-SSW.The expansion mode has changed from unilateral axial expansion to multi-directional cooperative expansion,but the focus of urban expansion has always been in the Northwest direction.Generally speaking,the evolution of urban external spatial morphology in Leshan City has undergone four stages in recent 20 years,namely "monocentric type","One-character type","diamond type","mass type".The evolution of urban external spatial morphology is continuous and progressive,orientation and direction anisotropy.(2)The main urban area is divided into three regions by using circle analysis method: core area,transitional area and fringe area.The evolution of urban main functional land is characterized by gradual circle change.Among them,the residential land expands gradually from the core area to the north and northwest;the commercial and public service land mainly distributes along the edge of the core area and transition area,and continuously advances to the north and northwest of the city;the industrial land withdraws from the core area,and the area of industrial land from the southwest of the transition area and the outside of the border area is growing.From 2002 to 2017,the evolution process of road structure in the main urban area is "cross"-"meter"-"radial+semi-circular"-"radial+multi-circular".(3)In addition to the constraints of natural geographical factors and the guidance of planning policies,and then SPSS is used to make principal component analysis and stepwise regression analysis of the socio-economic factors affecting the change of urban spatial morphology in the main urban areas from 2002 to 2017,and finally to determine the most important factors affecting urban morphological changes during the study period,namely,the natural geographical factors and the category of economic output value in the socio-economic factors.(4)Based on the summary of the achievements made in the social and economic construction,urbanization construction and ecological environment construction of the main urban area,this thesis puts forward an ecological concept for the current situation of urban land distribution in the main urban area,which is characterized by "scattered spread",crowded old cities,inadequate vitality of new cities,extensive utilization of urban space resources,cross-management of government departments,and inconsistent urban development.Four development proposals are put forward,namely,urban intensive development,optimization of urban spatial layout and industrial structure,optimization of urban comprehensive transportation system,complementary improvement of urban public services and municipal infrastructure,guidance of urban construction by "multi-integration",and strengthening the role of policy planning in guiding and intervening.