A Study On Urban Community Structure Evolution And Its Spatial Pattern Based On External Service Flow In Yangtze River Delta

With the rapid development of globalization,Informatization,and urbanization,agglomeration of cities has become an important spatial form for global competition and international labor division.The spatial organization of urban has also shifted from orderly scale structure to self-organized multi-center,nested structure.As a consequence,the direction of flows and intensity between cities has become the important basis for the inter-city cooperation.Previous scholars have conducted a great deal of research on the structure of urban agglomeration from different perspectives.However,the study on dynamic process in urban agglomeration space is still insufficiently.Most of the related researchers concentrated on the macro-level structure rather than the complex microscopic structure formed by different elements.Therefore,there are many vital issues remained to be further explored.For example,what are the core elements and core carriers in the conceptual framework of community structure?How to quantitatively reveal the status of community structure through the quantitative indicators in complex network analysis?How do the mechanism and law of urban community development change over time?The Yangtze River Delta(YRD)faces many challenges.Compared with the developed urban agglomeration of the United States and other developed countries,the internal relations of the YRD are not close enough and the cooperation among cities is relatively inadequate.The spatial structure of the YRD is staying at a critical period of development and integration.In order to formulate a valid strategy for space development,promote the effective operation of elements,optimize the structure and enhance the functions,it is necessary to explore the complex structures and evolution trend of YRD.Our research simulates the key interactions and connections among urban communities based on the urban economy basic theory and the urban flow model.First of all,three types of networks with different external service flows(producer,consumer,and public)were constructed through an interaction model,and then perform Complex Network Analysis to quantitativly examine the network.structures and the relationships between them.After that,according to the route of"Node-Contact-Pattern",we attempt to identify the evolving structure of YRD urban agglomeration by using Multi-dimensional Scaling analysis(MDS).Finally,we reveal the driving forces and mechanisms for YRD's structural evolution,provides theoretical support for the optimization of urban development pattern,and propose some measures to promote the integrated development of urban communities.The main research contents and conclusions are listed as following:(1)We analyzed the pattern and evolvement characteristics of point elements in YRD.Firstly,cities' external service capability is measured by the urban flow model,and statistically analyzed its changes in value and in spatial distribution during study period.The result shows that during the research period,the exrternal service of cities dominated by producer services.The value of urban producer services grew fastest and the value of public services grew slowly.Differences in the value of productive services and consumer services among cities show an increasing trend,and the distribution of public service values has become more balanced.By 2014,Nanjing and Shanghai are first-level service centers and Hangzhou is the only second-tier city.Rankings of Kunshan and Suzhou rose rapidly and their external service capabilities have significantly increased.(2)On the basis of the interaction theory,three types of external service communities were built.Using complex network analysis tools,this paper assessed the differentiation evolution of urban community structure from three aspects:overall evolvement features,node characteristics,vertical and horizontal structural features.The results show that the urban community structures under the three types of service function are both in the conversion stage-from a single structure to a complex multi-center structure.The differences among different structures are mainly manifested in the characteristics of the node size.the vertical variation of flows and the space concentration situation of the groups.In detail:1.The hierarchical structure of node producer service capability is fairly fixed.Shanghai,Nanjing and Hangzhou are diffusion nodes in this type of network.The hierarchical features in consumer service were obviously changed during 2003-2014.The public service values of nodes also experienced the process of unbalanced growth,but their distribution was relatively balanced.2.In the vertical structure,the network density,network efficiency,flow proportion and spatial distribution of each service network have obvious hierarchical heterogeneity with the increase of threshold.3.On the horizontal structure,the sub-group structure continued to be differentiate and reorganize.The specialization pattern of the external service network has Initially formed.(3)From the overall network and node functions,we discuss the structural relativity between three types of external service networks.And we build an identification system to detect and analyze the evolving structure patterns in different years.1.The results show that there is a difference in the degree of relevance among diverse community structures.Generally speaking,the relationship between producer service networks and consumer service networks is the highest,they are structurally convergent.2.The correlation coefficient of Public service network with the other two networks is declining.High-level nodes dominate the linkage between urban external service networks.3.Results of community structure refinement showed that the community structure under the producer service presented a transition from single-center to dual-core diffusion;and the evolution of community structure under consumer service was opposite.It replaced by a mononuclear diffusion structure.Compared with the first two types of service communities,the public service community has more core nodes and more dense networks,and the community structure evolves from single-center diffusive structure to multi-center equilibrium structure.(4)According to the characteristics of different types of urban communities and evolution trend in different periods,six key factors that promote the evolution of urban community structure were explored,including:the evolution of industrial structure,the division of urban functions,the location preference of different types of service industries,the construction of transportation infrastructure,the regional development strategy and institutional policies,the formulation of regional spatial development planning.At present,there are three problems exist,including:the degree of differentiation of service functions is relatively low;the node degree dispersion larger;sub-group structure is not yet mature,some outward links from sub-groups are weak.Based on the analysis of the problems and the mechanism,this paper proposes four optimization measures,including strengthening the guidance of urban service functions and avoiding the overlap of urban ecological niches;enhancing the vertical interaction of service networks and promoting the synergy of different levels of service centers;improving the convenience of service connection between cities,promote the spatial fusion of sub-groups;promoting the optimization of community structure and organization mode to a multi-center development pattern.