| The expansion of urban scale is the inevitable result of urbanization and industrialization.Urban development is an important symbol and epitome of economic and social development,and at the same time has played a huge role in radiating and stimulating regional economic and social development.Over the past 40 years of reform and opening up,Chinese urbanization construction and urban development have made remarkable achievements,driving the rapid growth of China’s economy.However,in the process of rapid urbanization,there have been situations such as one-sided pursuit of expanding the scale of the city,blindly expanding the urban framework,and disorderly expansion in a "spreading pie" style.There are serious problems such as "approved but not expropriated,expropriated but not supplied,supplied but not used" land in urban areas,and inefficient use of land in urban villages,which has led to the separation of "land urbanization" from "population urbanization",and even the phenomenon of "new towns" becoming "ghost towns" has attracted great attention from the society.The "14th Five-Year Plan" period is a transition period for China’s economic development,and China’s economy has shifted from a high-speed growth stage to a high-quality development stage.Promoting high-quality urban development is an inevitable choice for my country’s urban development in the future.Under this situation,the research on the dynamics and rationality of urban expansion,the analysis of the characteristics and driving factors of urban expansion,and the analysis of the problems existing in the process of urban expansion are of great significance to adjust urban land supply,make economical and intensive use of land resources,scientifically formulate urban planning and scientifically promote China’s urbanization and urban construction.Zhengzhou is the capital city of Henan Province,the core city of the Central Plains urban agglomeration,and the fastest growing city in the central region in the past 20 years.In 2018,Zhengzhou achieved three breakthroughs: the city’s regional GDP exceeded trillion yuan,the resident population exceeded 10 million people,and the per capita GDP exceeded 100000 yuan,and it was designated as one of the nine national central cities by the CPC Central Committee and the State Council.Taking the central urban area of Zhengzhou as the research object,using Landsat,DMSP / OLS and NPP / VIIRS multi temporal remote sensing data,using vbanui index method and supervised classification method,this study extracts the spatial-temporal information of dynamic expansion of built-up areas in the rapid development period of Zhengzhou central urban area from1995 to 2019.This study analyzes and calculates the expansion speed,expansion intensity,and expansion dynamics of urban built-up areas in the central urban area of Zhengzhou.The urban gravity center method and the wind rose diagram method are used to analyze the dynamic characteristics of the urban gravity center migration and the main direction of urban expansion.The compactness and fractal dimension index are used to quantitatively analyze the boundary shape of urban expansion.The built-up area of GDP per unit of secondary and tertiary industries and the elastic coefficient of urban expansion are used to analyze the rationality of urban expansion.The principal component analysis was used to analyze the main drivers of urban expansion.The main findings of this study are as follows:(1)Using Landsat satellite image data,the supervised classification method can be used to identify urban and village construction land,but it is difficult to effectively distinguish urban land from suburban village land.DMSP/OLS,NPP/VIIRS night light image data can distinguish urban and suburban rural settlements,but the geometric recognition accuracy is low.The superposition analysis of the extraction results of the two can effectively eliminate the suburban village land.The comparative analysis of the extracted built-up area information with statistical data and high-precision remote sensing data sampling shows that the scale error of the extracted built-up area is less than 5%,and the spatial consistency is greater than 90%.The extraction of the built-up area values and spatial information is reliable,and in the absence of early statistical data and high-precision remote sensing data,it is a feasible method to study the dynamic changes of urban expansion.(2)From 1995 to 2019,the urban built-up areas in the central urban area of Zhengzhou expanded from 103.36km~2 to 577.82km~2,with an average annual expansion of19.77km~2 and an average expansion intensity of 1.94%,which is a type of rapid expansion.Since 2000,it has entered a period of rapid expansion,which increased from the previous average annual expansion of 5.97km~2 to 23.40km~2.During the period,affected by the global financial crisis in 2008 and macro-control,the average annual expansion was 17.36km~2 from 2005 to 2015.From the perspective of administrative areas,Guancheng Huizu District,Jinshui District,and Zhongyuan District have the fastest expansion rates,5.20km~2/year,5.06km~2/year,and 4.62km~2/year,respectively.The expansion rates of Huiji District and Erqi District were relatively slow,at 2.47km~2/year and 2.20km~2/year,respectively.Jinshui District,which has a fast urban expansion rate,has a relatively low expansion dynamic rate,only 12.96%.Huiji District,which has a relatively slow urban expansion rate,has a large expansion dynamic rate,with a value of69.73%,which reflects the balance of the various administrative regions that go hand in hand and come from behind.developmental characteristics.(3)From 1995 to 2019,the overall urban center of gravity in the central urban area of Zhengzhou has shifted to the east,reflecting the strong development of Zhengzhou to the east,which is in line with the integrated development strategy of Zhengbian and the construction plan of Zhengdong New District.However,the overall migration range is not large,and it shows the characteristics of urban extensional expansion.This spatial expansion feature is the result of the superposition of the two elements of the integrated development strategy of Zhengzhou and Bian and the balanced development needs of cities in various administrative jurisdictions.It shows that the direction of urban spatial expansion and the government,the urban development strategies of the two countries are basically consistent,and the urban development is basically in an orderly and controllable state.(4)From 1995 to 2019,the scale of urban built-up areas in the central urban area of Zhengzhou increased by 459.04%,the GDP of the secondary and tertiary industries increased by 3330.83%,the total population increased by 176.47%,and the per capita urban land area increased from 54.78m~2 to 110.78m~2.Urban expansion is basically consistent with the growth trend of population and urban economy,and the per capita urban construction land is within the planned quota(basically consistent with the planned quota of 95m~2),indicating that the urban expansion in the central urban area of Zhengzhou in the past 24 years is basically reasonable and basically healthy.However,the urban expansion rate of Huiji District was significantly higher than the population growth rate from 2010 to 2015.Therefore,the urban land supply should be reduced moderately in Huiji District to attract population inflows.(5)The quantitative analysis of the driving force of urban expansion shows that economic and demographic factors have an important driving effect on the urban expansion of central urban area of Zhengzhou from 1995 to 2019.The per capita disposable income of urban residents,investment in fixed assets,output value of tertiary industry and total population are the main factors of urban expansion in Zhengzhou central urban area from 1995 to 2019,and their weight coefficients in the principal components of driving factors of urban expansion are 0.179,0.177,0.173 and 0.171 respectively.In addition,urban expansion in the central urban area of Zhengzhou was also affected by transportation construction,natural conditions and the impact of government decisions. |
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