Research On The Process And Mechanism Of Spatial Evolution In City Region

City region refers to the urban assemblage system with a certain structure,form and function formed by all cities through extensive and close socioeconomic links in a specific spatial range when urbanization and industrialization develop to a certain level.China has rushed into the critical stage of rapid development of city region,in the future,metropolitan area and urban agglomeration will take the main growth pole of China’s economic development.At present,China has preliminarily formed a spatial pattern of city region by the coordination development of central city,metropolitan area and urban agglomeration,however,there exists practical problems in identification,planning and management.This paper focused on the process and mechanism of spatial evolution of city region,emphatically discussed the interactive relationship between central cities,metropolitan areas and urban agglomerations,and followed by the construction on the theoretical framework and evolution model of spatial evolution of city region from three aspects:spatial structure theory,evolution stage theory and evolution dynamics theory.The form and process hypothesis,threshold effect hypothesis and fusion mechanism hypothesis were proposed.The three major city region of the Yangtze River Delta,Pearl River Delta and Beijing-Tianjin-Hebei were taken as the specific research objects.The interurban gravity model was applied to analyze the process of city regional evolution,the panel data threshold model for the analyzing of the threshold effect of city regional economic growth on spatial structure,and the spatial metrology model for the effect of city regional industrial cluster on economic efficiency at different morphological stages.The below four main conclusions were obtained:First,metropolitan area and urban agglomeration are the manifestations of city region in different stages of evolution.Metropolitan area contains obvious single-center peripheral structure,while urban agglomeration belongs to typical multi-center network structure.There are significant differences in internal connection,core function,formation mechanism and equilibrium state between the two.There is a progressive relationship for metropolitan area and urban agglomeration:the metropolitan area is formed by the convergence of central cities and surrounding cities,while urban agglomeration is formed by the integration of different metropolitan areas.According to the form of urban area,the evolution process can be divided into three stages(the central city stage,the metropolitan area stage and the urban agglomeration stage)and two processes(the aggregation process and the fusion process).The city region evolves from metropolitan form to urban agglomeration form and requires specific conditions that is simultaneously influenced by multiple factors.Second,city regional evolution is a process of morphological upgrading and structural change,which following the evolutionary path of"central city-metropolitan area-urban agglomeration".Based on the modified intercity gravity model,the regional spatial connections of the three major cities in China in 1998,2008 and 2018were calculated,respectively,and the spatial connection strength was characterized by the intercity connection.The image results showed that there are indeed phenomena and trends of urban agglomeration formed by the fusion of two or more metropolitan areas.The spatial structure of the three major cities was analyzed by complex network analysis tools,which shows that the current Yangtze River Delta and Pearl River Delta city region have entered the stage of urban agglomeration form,showing a trend of networking and equalization;the Beijing-Tianjin-Hebei urban area is still in the stage of continuous mature metropolitan area form,and the spatial circle structure is more obvious.By comparing and analyzing the regional evolution of the three major cities,it is found that the regional evolution of cities contains features of phases,gradualness,path dependence,self-organization,complexity and uncertainty,etc.The fundamental impetus of city regional evolution lies in urban growth,the necessary condition lies in the improvement of transportation network,the limiting factor is regional segmentation and the general trend is networking and multi-centralization.Third,city regional economic growth has a single threshold effect on the evolution of spatial structure with urbanization level and traffic connection level.Based on the panel data of three large city region in China from 1998 to 2018,the results of threshold regression model show that the threshold values of urbanization level and traffic connection level are 53.82%and 27,700 tons/km~2,respectively.After crossing the relevant threshold value,the centrality and Gini coefficient of city region is significantly different with the change of economic growth,which reflects the phenomenon that city region change from metropolitan area form to urban agglomeration form to a certain extent.Among them,the years of crossing the threshold value of urbanization level in the city region of the Yangtze River Delta and Pearl River Delta are 2008～2009 and 2002～2003,respectively,and the years of crossing the threshold value of transportation connection level are 2009～2010 and 2008～2009;the years of crossing the threshold value of urbanization level in the city region of Beijing-Tianjin-Hebei are 2014～2015,without crossing the threshold value of transportation connection level so far.It can be seen that the city region of the Yangtze River Delta and Pearl River Delta have entered the stage of urban agglomeration form,while the city region of Beijing-Tianjin-Hebei are still in the stage of metropolitan area form.Fourth,the spatial evolution of city region abides by the chain dynamic mechanism of"industrial cluster→economic efficiency→spatial form",that is,industrial cluster and diffusion between metropolitan areas promotes the improvement of the overall economic efficiency of city region,and then promotes the integration of metropolitan areas to form urban agglomeration.Based on the panel data of city region in the Yangtze River Delta from 1998 to 2018,the results of spatial lag model analysis show that both productive service industry and domestic service industry cluster have a positive promoting effect on the economic efficiency of city region,while manufacturing cluster exists a negative effect on the economic efficiency at the metropolitan form stage.However,with the improvement of metropolitan opening,the negative effect of manufacturing cluster on the economic efficiency gradually weakens or even turns into a positive effect.Therefore,it can be judged that in the process of urban agglomeration formed by metropolitan integration,and the diffusion of manufacturing industry is the most critical decisive variable.Furthermore,with the cluster of productive and living service industries,the cluster and diffusion of different industries trigger the industrial association and cooperation of different metropolitan areas,besides,the advanced nature of industrial structure promotes the evolution of city region to higher forms.