Study On Temporal And Spatial Characteristics And Influencing Factors Of Urban Expansion In Yangtze River Delta Urban Agglomeration

With the rapid economic growth,China’s urbanization process continues to accelerate,urban land is highly developed and utilized,and the scale of built-up areas continues to expand.In this process,a series of problems such as too pursuing speed and ignoring the sustainable development of urbanization begin to appear in urban expansion.Some urban development even shows the trend of low-density expansion,which has curbed economic growth to a certain extent.At this stage,China ’ s economy has changed from high-speed growth to high-quality development.Urban expansion also needs to be guided by high-quality,alleviate ineffective low-density expansion,realize the organic renewal of the city and optimize the urban development space.Therefore,analyzing the evolution characteristics of urban expansion in time and space and exploring its influencing factors are of practical significance for urban sustainable development.This paper selects Landsat satellite remote sensing data in 2000,2010 and 2020,and uses ENVI and Arc GIS 10 2 and other software extract the built-up areas of 26 cities in the Yangtze River Delta urban agglomeration,analyze the temporal and spatial laws and characteristics of the urban built-up area expansion of the Yangtze River Delta Urban Agglomeration by using the indicators such as urban expansion speed,compactness,intensity,center of gravity change,azimuth change and spread index,and then introduce the geospatial detector to reveal the influencing factors of the urban expansion of the Yangtze River Delta urban agglomeration.The results show that:(1)From 2000 to 2020,the compactness of the external form of the Yangtze River Delta urban agglomeration decreased from 0.04 to 0.03 and remained the same,and the fractal dimension decreased from 1.79 to 1.77 and then to 1.76.It can be seen that the urban expansion structure of the Yangtze River Delta urban agglomeration has not changed greatly from 2000 to 2020,and the urban boundary is gradually regular.On the whole,the urban expansion is relatively stable,cities in the Yangtze River Delta urban agglomeration showed the law that the compactness index of larger cities was lower and the fractal dimension was higher,and the compactness index of smaller cities was higher and the fractal dimension was lower,that is,cities with large urban scale had more complex spatial form and lower degree of intensification,while cities with small urban scale had relatively simple urban spatial form,high degree of intensification and high degree of compactness;(2)The focus of urban expansion of26 cities in the Yangtze River Delta urban agglomeration is in Wuxi,Jiangsu Province.From 2000 to 2010,the cities of the Yangtze River Delta urban agglomeration expanded to the West and South on the whole.In terms of quantity,more cities migrated to the east than to the west,and more cities migrated to the north than to the south;(3)The expansion direction of each city presents two expansion characteristics,namely,multi-directional expansion and single direction expansion.The number of multi-directional expansion cities is more.On the whole,the coastal cities in the Yangtze River Delta urban agglomeration tend to expand in the coastal direction,while other cities tend to expand in the direction of high-level cities;(4)The urban sprawl degree of urban agglomeration in the Yangtze River Delta has spatial heterogeneity.The sprawl degree of mega cities is relatively low,and the sprawl degree of small and medium-sized cities is high.Most cities with relatively high degree of sprawl are concentrated in the north of the Yangtze River Delta Urban Agglomeration and Jiangsu Province.The distribution of degree of sprawl in Zhejiang Province is relatively balanced,and the score of degree of sprawl in Anhui Province is relatively unbalanced;(5)GDP,the output value of the primary industry,the output value of the secondary industry,the output value of the tertiary industry,the resident population,the total retail sales of social consumer goods,real estate development investment,the average wage of non private employees,grain output,fiscal expenditure and fiscal revenue all have a significant impact on the urban expansion of the Yangtze River Delta urban agglomeration,and the distance from the river,altitude and railway also have a great impact on the urban expansion of the Yangtze River Delta urban agglomeration,Generally speaking,socio-economic factors are the main driving force of urban expansion of urban agglomeration in the Yangtze River Delta.Natural driving factors have a certain impact on urban expansion,but the degree of impact is less than socio-economic factors.