Urban Location And Urban Expansion:Evidence From The Yangtze River Delta Urban Agglomeration

Since 1980s,China's urbanization has gained speed.Urban agglomeration featuring closely linked cities,hierarchical structure and network organization in a certain geographical area has gradually formed around the nation.At present,China is working out the strategic planning of urban spatial development with urban agglomeration as the main form.Researching urban joint expansion of the whole urban agglomeration provides us with a new perspective to study regional coordinated development.Study on mutual relationship between urban location and urban expansion serves as a reference for the planning of the Yangtze River Delta urban agglomeration and the regulation of urban expansion of other urban agglomerations.On the other hand,it is of great significance to reveal the complicated coupling relations between urban expansion and different network organization within the urban agglomeration.This article takes Yangtze River Delta Urban Agglomeration(YRD)as study area.Build-up land area was obtained from Landsat remote sensing data in 1980,1990,2000,2010,and 2013 to study spatio-temporal dynamics of city-size distribution of the urban agglomeration.Urban traffic location was measured by the accessibility to regional core cities and accessibility of traffic network.Urban economic location was measured by urban flow model and economic flow model.Then the urban location of each city was comprehensively measured by traffic location and economic location.Based on study of urban expansion and urban location,interactive relationship between urban location and urban expansion was quantitatively analyzed and multiple linear regression model was modelled.The main conclusions are as follows.(1)City size distribution of build-up land in YRD is more balanced than what is expected of Zipf s law.City-size distribution tended to be concentrated before 2000 and dispersed after 2000.After urbanization entered into a rapid development stage in 2000,city-size distribution showed a spatial convergence trend.Meanwhile,Gibrat's law doesn't hold any longer,small and medium-sized cities expanding faster.(2)Traffic location among different cities tends to be balanced development,while the weight of sub-regional central cities in economic location is constantly increasing.The link between location indicators(traffic location and economic location indicators)and urban expansion intensity showed a trend of first increasing and then decreasing.After 2000,cities with a low level of traffic location and economic location expanded faster and exhibited a convergent trend.(3)Results of multiple linear regression model show that:During 1990-2000 when urban expansion began to speed up,the accessibility of traffic network has a significant influence on the intensity and speed of build-up land expansion,and urban flow intensity is positively associated with built-up land expansion intensity.During 2000-2010 when urban expansion entered a rapid development stage,the accessibility of traffic network has a significant influence on the intensity of build-up land expansion.Urban flow intensity is the major divers of urban build-up land among location indicators between 2010 and 2013.Meanwhile,the accessibility of regional core cities was negatively associated with the speed of urban expansion,cities far away from core cities growing faster.(4)Economic indicators are the major drivers of urban expansion in the whole study period.When urbanization reached a certain degree,tertiary industry development level linked more closely with urban expansion intensity.Resident population density is the major driver of the speed of urban expansion in each phase.The greater the added value of resident population density is,the more compact urban development tends to be.Therefore,urban build-up land expands at a much slower rate.