Research On Identification And Driving Factors Of Physical Urban Shrinkage In The Yangtze River Delta Based On Multi-source Data

With China's economy entering the new normal,the phenomenon of local contraction in the process of rapid urbanization has attracted widespread attention.The Yangtze River Delta is one of the most dynamic regions in China.Due to the uneven development between regions,the growth of population and economy in the advantageous areas has led to the partial shrinkage of population loss in the disadvantageous areas.A comprehensive analysis of the shrinking cities in the Yangtze River Delta is of great value for the rational formulation of urbanization and regional sustainable development strategy.This paper takes the physical urban area as the study unit,and conducts research on the identification and driving factors of physical urban shrinkage based on multisource geographic big data in the Yangtze River Delta from 2010 to 2018.Firstly,the kernel density cumulative distribution function of POI data was used to identify the spatial extent of the physical urban area in the Yangtze River Delta.Secondly,a multidimensional feature database was created based on geographic data such as statistical population,land use,night lighting,POI,road network,etc.,and inputted into the random forest model to obtain spatialized population data of 2010 and 2018 at the 1km grid scale in the Yangtze River Delta.Then,the grid population data of 2010 and 2018 were extracted by the identified physical urban area,and change rate of resident population was used as a measurement method for shrinking cities to reveal the urban shrinkage of the Yangtze River Delta from 2010 to 2018.Finally,the paper constructed the geographical weighted regression model to analyze the driving factors of physical urban shrinkage and put forward corresponding countermeasures and suggestions.The main conclusions obtained are as follows:(1)Based on POI data,847 physical urban areas were extracted from the Yangtze River Delta,with an area of 15,351km~2.In contrast to the traditional administrative cities,the larger physical urban areas are mainly located in the eastern coastal areas,while the smaller ones are in the west.The scale distribution of the identified physical urban areas obeys Zipf's law,and there is also a significant positive correlation with the verification data(R~2=0.94),indicating that the physical urban areas extracted based on POI data are reliable and effective in this paper.(2)The overall fitting accuracy of the population spatialization model constructed based on the multi-dimensional feature database and the random forest algorithm is95.47%.Comparing the accuracy of the population spatialization results in this paper with the verification datasets and statistical population data,the results show that the population spatialization results obtained based on the random forest model have higher simulation accuracy.Based on the above training model,the population spatial distribution of the Yangtze River Delta in 2018 is predicted,and the results still have high fitting accuracy.Compared with the verification datasets,this result has certain advantages in various accuracy verification indicators and is significantly positively correlated with statistical population data.(3)Based on the physical urban area and population spatialization data,88 physical shrinking cities were identified by using the population change rate,with an area of 2253.59 km~2,accounting for 14.68% of the total physical urban area.Except for Shanghai,provincial capitals,southern Jiangsu and southeast coastal areas of Zhejiang Province,there are some shrinkage phenomena in other areas.Among them,Jiangsu Province and Anhui Province have the same number of shrinking cities,39 each,accounting for 86.8% of all shrinking cities.They are mainly distributed in northern Jiangsu,central Jiangsu,northern Anhui and southern Anhui;Zhejiang has the least number of shrinking cities,with only 10,in the southwest of Zhejiang Province,mainly in Lishui city.(4)Comprehensively considering the actual situation in the Yangtze River Delta region,the driving factors of physical urban shrinkage are explored by means of geographic weighted regression analysis from the three aspects of urban economy,urban scale and urban facilities.The results show that different influencing factors have different intensity of influence on urban shrinkage,and the combined effect of multiple factors has caused urban shrinkage.For shrinking cities,solutions can be formulated by strengthening regional cooperation,advancing rational guidance of government policies,and increasing investment in urban infrastructure,so as to provide decisionmaking suggestions for the healthy and sustainable development of shrinking cities.