Research On The Measurement And Influencing Factors Of China’s Three-Dimensional Expansion

The rapid development of urban over-expansion has disturbed the urban ecosystem to a large extent,which pose an unprecedented challenge and threat to human survival.The concepts of "compact city","urban complex" and "three-dimensional city" have been put forward constantly,which shows that the compactness of urban space has been continuously improved.Therefore,the incorporation of three-dimensional spatial measurement into the urban expansion measurement system plays an important role in understanding the extent of urban expansion and in its regulation and governance.Based on the urban three-dimensional spatial data,this paper studies the three-dimensional urban expansion measurement system applicable to cities of different sizes,which is mainly divided into four parts:The first part is to construct the theoretical analysis framework of urban three-dimensional expansion.This part develops a theoretical framework system from the urban three-dimensional expansion mechanism and the regulation theory.The second part quantitatively reveals the spatial and temporal distribution of China’s three-dimensional urban expansion from 1990 to 2018,and quantitatively measures the three-dimensional expansion from three dimensions: density dimension,shape dimension and ecological dimension.The third part studies the driving factors of urban three-dimensional expansion.We selected 13 influencing factors from four aspects of nature,society,economy and government,and calculated the urban expansion index to identify the influencing factors of urban three-dimensional expansion.The fourth part,from the three levels of monitor-driven and regulation-governance,puts forward suggestions on macro-control of urban three-dimensional expansion.The main conclusions are as follows:(1)From the perspective of density dimension,the composite growth rate of the national average urban volume from1990 to 2000,from 2000 to 2010 and from 2010 to 2018 was 5.18%,4.12% and3.90%,respectively.The growth slowed down gradually.In the past 29 years,the three-dimensional expansion of cities in the western region was the largest(4.1%),the eastern region was the middle(3.46%),and the central region was the smallest(3.28%).From the perspective of form dimension,urban expansion in northern China has gradually moved from expansion to compactness,and urban space utilization efficiency has improved,while the situation in the south was opposite.In addition,the expansion pattern of urban patches in all regions of China is mainly marginal,and enclaves are more in the central and eastern regions.From the perspective of ecological dimension,taking 2010 as the turning point,the blue-green space showed an obvious decrease trend from 1990 to 2010,and an obvious improvement trend from 2010.(2)The three-dimensional expansion of Chinese cities is the result of the indirect effect of natural conditions and social progress,as well as the primary drive and direct effect of economic development and government behavior.(3)There are differences in the degree of expansion of cities under two-dimensional and three-dimensional analysis,with 38.1% of cities expanding more under two-dimensional analysis and 5.4% of cities expanding more under three-dimensional analysis.(4)This study believes that when analyzing the expansion process of the rapidly developing small-scale cities and most large-scale cities,it should be carried out from a multidimensional perspective to obtain a more comprehensive understanding of the urban expansion process.