Analysis On The Characteristics Of Urban Spatial Expansion Of Northwest China Cities

Urban expansion is the frontier and hotspot of global change research.With the rapid development of GIS and RS technology,land use information has become an important research content of city expansion,which acquired by RS technology.Based on the strategic concept of "one belt and one road",taking the main provincial capital cities of northwest China cities as the research object,through the study of the expansion and development of the northwest urban agglomeration,analyze the change rule,find out the internal reasons,put forward reasonable and efficient plans for urban expansion and land use,and reduce the impact of human activities on the environment,It is of great significance for maintaining the stability of ecosystem and the sustainable development of land resources.At present,there are many studies on urban expansion and its driving forces,however,most of them neglect the interaction between factors.At the same time,it is less that is the comparative analysis of the influence of the interaction of research factors among different cities on urban expansion.To solve the above problem,this study takes Xi'an,Lanzhou,and Urumqi of three city group as the study area;explore the expansion of the of northwest China cities space evolution characteristics in 1990-2015.Firstly,the characteristics of urban construction land expansion intensity,expansion type,expansion elasticity,and ecological landscape are comprehensively analyzed by RS and GIS technology.The urban expansion changes of Xi'an,Lanzhou,and Urumqi from 1990 to 2015 were studied.It reveals the dynamic changes of the scale,time and space of urban expansion in Xi'an,Lanzhou,and Urumqi.Then used the geographical detector,explored the natural and socio-economic driving forces factors that cause the urban expansion changes of the three major provincial capitals Finally,a comparative analysis is carried out,and the results are as follows:(1)In the past 25 years,the construction land of Xi'an city,Lanzhou city,and Urumqi city have shown a strong expansion trend,Especially in 2005-2010;urban expansion was the most significant.The expansion strength performance in the space: Xi'an city is stronger than Urumqi city and Lanzhou city,and Urumqi city is stronger than Lanzhou city.This is closely related to the national macro-policies such as the development of the western region,but also affected by the topography and other conditions.(2)The development of three big cities is mainly marginal expansion,followed by filling expansion,while enclave expansion shows a small fluctuation in different years,but the overall proportion is small.At the same time,the three big cities all present a circle-type development pattern,in which the original construction land and the built-in land,the marginal land and the enclave land are distributed from the inside to the outside in turn.Inaddition,the type of urban development shows a trend of transition from marginal rapid expansion to an intensive development,after 2010,which coincides with the evolution process of extensive development before intensive development in the process of urbanization in China.(3)The expansion elasticity of three big cities reveals that the whole northwest cities are expanding rapidly.Among them,Lanzhou city's land expansion and population growth are balanced.Xi'an city's land expansion is much faster than population growth,while Urumqi city's is between them.The expansion elasticity of the three big cities is mainly guided by both topographic factors and policy factors.(4)Three big cities show different patterns of urban expansion eco-landscape in different periods.Generally speaking,Xi'an has the highest compactness,Lanzhou has the most obvious fragmentation,and Lanzhou has the largest urban complexity index under the influence of complex terrain conditions.(5)Follow is obtained by using factor detector method of Geo Detector The road area,city population,total investment in fixed assets and other driving factors have a significant influence on the expansion of Xi'an City,Financial expenditure,urban population,Road is,and other driving factors have a significant impact on urban expansion in Lanzhou city.The staff wages,the road area,city population,and other driving factors have a significant influence on the expansion of Urumqi city.Through interactive Interaction detector method,it is concluded that the interaction among the driving factors has a significant impact on the urban expansion of the three cities,which is manifested in the double factors enhancement.The interaction between the proportion of secondary and tertiary industries and the area of roads has the greatest impact on the urban expansion of Xi'an,and the interaction between the proportion of secondary and tertiary industries and the number of colleges and universities has the greatest impact on Lanzhou.The interaction between the proportion of secondary and tertiary industries and the area of roads,the interaction between wages and expenditure of working staff,the interaction between the proportion of secondary and tertiary industries and the number of colleges and universities has the greatest impact on the scale of the impact is relatively strongest.