Spatial-Temporal Change And Driving Force Analysis Of Built-up Area In Northwest China Based On Night Light Data

The backward development of urbanization in Northwest China has been a long-standing problem for the government,which has seriously restricted the development of social economy in China,and is an important manifestation of unbalanced regional development in China.Although the urbanization level of Northwest China still lags behind other regions,it has obvious development compared with that before 2000.It is very important to understand the dynamic changes of urban expansion in Northwest China during this period,to reveal the mode of urban expansion,to clarify the driving force of urban expansion,to promote the development of urbanization and regional coordinated development in Northwest China,and to formulate urban planning and development strategies reasonably significance.Nighttime lighting data record human nighttime activities and reflect the range of human activities.It is an important data source for studying urban expansion in recent years.The nighttime lighting data structure is simple,easy to obtain,easy to process,more suitable for large-scale area research.This paper uses the invariant target area method to correct the data of DMSP/OLS and NPP/VIIRS,and obtains the long-time night light images of Northwest China from 2003 to 2018.Combined with the existing algorithm,a new method is proposed to extract the built-up area from the night light images over the years.From the speed,intensity and center of gravity of the expansion of the built-up area,this paper studies the temporal and spatial characteristics of the built-up area,and analyzes the mode of urban expansion through the evolution of urban spatial form.From three aspects of population,economy and transportation,combined with statistical data and built-up area,single factor analysis and multi factor analysis are carried out to determine the driving force of urban expansion in Northwest China from 2003 to 2018.The results show that:(1)the area of the built-up area extracted by the marked watershed algorithm of the partition reconstruction is close to the statistical data,the area of the broken spots is small and the accuracy is high.The marked watershed algorithm of the partition reconstruction is a method suitable for extracting the built-up area from the night light image.(2)The speed and intensity of urban expansion in Northwest China are increasing,and the location of urban center of gravity is constantly moving to the southeast.(3)The expansion mode of cities in Northwest China from 2003 to 2018 is mainly divided into two types: the regions with early urbanization development need to go through a process,which is to expand steadily around first,then generate fragmentation from the inside while expanding,and finally generate new construction area spots around the built-up area;small cities with late urbanization generally experience a complex dynamic process,which is to expand in a specific direction first,then new built-up areas,continue to expand around,and gradually integrate the spots,finally expand around.(4)The increase in the total value of the tertiary industry,the adjustment of fixed assets,the increase in the area of urban roads at the end of the year,the adjustment of the total retail sales of social consumer goods,and the increase in the average annual total population are the main driving forces for urban expansion in the northwest region from 2003 to 2018.