Effects Of Urban Expansion Patterns On Urban Vitality And Its Enhancement

With the continuous promotion of urbanization in China,urban expansion and its consequences,such as the imbalance distribution of urban social and economic factors,and the inefficient use of land resources,have attracted the continuous attention of urban planners and administrators.The goal of urban development and planning has also shift from the traditional pursuit of land economy to rational and sustainable development,and to the improvement of urban quality.In the transition period of urban development,higher requirements are put forward for the management and control of urban expansion,urban vitality and quality are promoted to be the goal of urban development.It is critical to grasp the law and stage of urban expansion.Current studies can't provide a comprehensive and objective view of urban physical development,and have not taken vitality as a measure for expansion efficiency to quantitatively explore the influence mechanism of urbanization stages on urban vitality,as to guide the orderly implementation of urban planning.To make compensation on the current problems of "more mixing,less logic" on urban expansion measurement index system,and "more guidance,less quantification" on the influence mechanism of urban vitality,this study takes the 1796 community units of Wuhan metropolitan as the research area,to identify the macro and micro physical expansion stage and pattern.Then explores the influencing mechanism of urban expansion patterns on urban vitality.Finally,regulations and control guidelines for different expansion patterns to promote vitality are formulated.The research contents and main conclusions are as the following four aspects.(1)Multi dimension and multi-scale urban expansion index system and expansion modesAccording to the stage of urban physical development,an urban expansion measurement index system is constructed based on physical elements of land cover,road,building and facilities,and the social,economic and political effects from the five dimensions of "urban development-urban form-urban function-urban activity-effectiveness of expansion" by separating physical environment from social economic factors.The system covers three scales of city level,county level and community level.From 1989 to 2017,Wuhan experienced three stages of "industrial development period,industrial upgrading stage and structural optimization period".The spatial pattern of urban development is consistent with each round of planning,while the scale of urban land is much more than the planning expectation.In the era of “industrial development”,the average annual expansion speed of land use and construction for Wuhan metropolitan area is quite fast,as well as building density.The city is mainly expanded horizontally,construction focuses on public infrastructure and public service facilities in the main urban area and Zhuankou,Yangluo and Guanshan industrial areas;the urban expansion is mainly marginal and leaping,with low compactness,complex shape,and extending to three-dimensional space.During the industrial upgrading period,the average annual expansion speed of land use and construction lowered down,as well as building density,development focus on the residential clusters in the main city,and the construction of satellite towns outside.A multi-center cluster structure is formed by urban construction sparsely and the compactness was significantly reduced,while the shape turned to be complicated.In structural optimization period,the expansion speed of land use and construction,the construction intensity increased substantially.The industries of the main city moved out to the new city clusters.Construction was centralized and the structure of six new city clusters was formed.The compactness increased and the shape tends to be simplified,the density of road crosses and average building height increased greately.Except for green land,the proportion of other laduse conformed to the planning standards,while the overall level of land diversity and the building diversity improved,especially in Xudong,Nanhu,Guanshan and other areas,which indicated that the distribution of functional buildings in this area is uneven,which may lead to problems such as single function,lack of vitality,traffic congestion,etc.Except for primary and secondary school,the accessibility of other facilities increased.The social benefit of urban expansion was relatively low.The economic benefits of land use expansion was on a rise,as well as for the policy benefits,except for green land.The community-based urban expansion pattern of Wuhan metropolitan area is divided into seven categories.Type I are mature residential communities.Type II is near water industry development zone.Type III are mature communities with complete facilities.Type IV are the urban non centralized construction area s.Type ?are industrial cultivation area of new city clusters.Type VI are highly compact but single functional residential communities.While type ? are residential communities with complete but low-quality facilities.(2)Measurement and evaluation of urban vitalityBy ultilizing internet big data such as catering,hotel accommodation,scenic spot recreation and business office,the agglomeration level of various basic activities of residence,employment,transportation and recreation,is measured respectively to form the comprehensive vitality of the city.Urban vitality shows obvious axis and circle distribution characteristics.By implying the theory of urban vitality,this paper constructs an index system of community-level vitality measurement from four dimentions of "mixing degree-block scale-building inclusiveness-agglomeration degree",and calculates the community comprehensive vitality index by applying factor analysis model.By the utilization of correlation test model,a strong correlation is discovered between urban actual vitality and the comprehensive vitality index based on the urban vitality theory.Among the four dimensions,agglomeration degree is more important than average stages and diversity of building stages,then diversity of building(including house price and age),the next is street scale,and mixing degree(population agglomeration and building)is as follows.By applying correlation test,the two vitality indexes are highly consistent.Devirations locate in some newly urban clusters or newly constructed but high qualified areas.Human aggregation needs to go through a slow and continuous spontaneous process.The index from urban vitality construction theory is more inclined to the construction elements while the index of check-in data focuses on human activities.Therefore the later will lag behind the construction index based on theory.(3)Effects of urban expansion mode on urban vitalityThe evaluation index system of urban vitality is constructed from the aspects of the physical environment characteristics of each dimension of urban expansion and the external environmental factors such as social economy.By applying the correlation test,eight external environmental factors are found significantly related to urban vitality,among which population density and average house price have the strongest correlation coefficient.Except for the index of construction intensity,the proportion of green land,the accessibility of tourist facilities and employment facilities,the rest indexes of urban expansion are all significantly related.Considering the spatial autocorrelation of urban vitality,the spatial lag model(SLM)is applied and 15 factors are found significantly affect urban vitality,which can explain 91.34% of urban vitality,while the conduction effect can explain 83% of urban vitality.The influence degree of each urban expansion dimension on urban vitality is: urban activity dimension > urban development dimension > urban form dimension > urban function dimension,and the last is social and economic factors.In terms of specific indicators,among the promotion factors of urban vitality,the accessibility commercial facilities at street level > increment of building area > proportion of commercial landuse / accessibility of public transport facilities > construction intensity / building density / accessibility of parks /heterogeneity of housing prices > accessibility of lakes;while among the factors that inhibit urban vitality,building density increment > accessibility of commercial facilities at community level > building pattern index > house price diversity > road pattern index > building area.(4)Research on the differential regulation of community vitality promotion based on urban expansion patternThe index system of urban vitality regulation is constructed from the four dimensions of urban expansion model and socio-economic dimension.By ananlysing the clustering characteristics of regulatory indicators under each level of vitality intensity,and the intensity distribution within each range of indicator value,the influence threshold of each regulatory indicator is determined.Among them,the building density of urban development dimension has a positive correlation with a threshold of 20%.The two weakening factors of urban form dimension have been tested and become the promoting factors of high vitality level,with the influence threshold range of 30-150 road ntersections per square kilometers of road density intersections and the threshold of building form index is 5.The proportion of commercial landuse of urban function dimension shows an unstable threshold effect,ranging from 10% to 70%.For the activity dimension,accessibility of public bus and commercial facilities at street level show threshold effect,with value of 0.9 and 0.55 respectively.In the socioeconomic dimension,the diversity of house prices does not show a threshold effect,but the heterogeneity of house prices shows a significant instability effect,the threshold range is 500-2000 yuan per square meter.According to the characteristics of urban vitality under the mode of urban expansion,this paper puts forward differentiated suggestions for improving the vitality conformed to urban planning,so that the community construction in different stages and modes of urban expansion can be carried out in a compliant and orderly manner on the premise of ensuring the level of vitality.For the type IV Urban Non-centralized construction areas with low vitality level,it mainly focuses on protective development and rational utilization of ecological resources.In order to promote the effective use of country parks,it mainly focuses on the construction of infrastructure and tourism supporting facilities.For class II Near-water Industrial Development Zone with medium vitality,priority should be given to the development of public transport,followed by strengthening the commercial service level,introducing diversified residential products to enrich the diversity of housing prices and attract people.For the main industrial cultivation areas of class V in the new city clusters,except for nearwater,other characteristics are relatively consistent with type II,and the function and public service accessibility should be improved orderly.For type VI of compact residential communities,the commercial facilities are seriously insufficient.We should pay attention to improving the accessibility of public transport and street level commercial facilities,and introduce diversified residential products to enrich housing prices.For type VII communities with complete but low-quality services,we should improve the service quality.For old communities in urban area,mainly improves the service quality by means of urban renewal or upgrading the capacity of facilities.In the new urban area,we can improve the service quality by means of constructing high-level facilities or improving the traffic.