Study On The Urban Three-dimensional Expansion Based On Multi-source Data

The contradiction between the rapid urbanization of the population and the shortage of urban land and the increasingly complex urban functional requirements have shifted urban development from two-dimensional expansion to three-dimensional expansion.The height and volume of urban buildings and the terrain where urban development is located have generally risen.The research on the three-dimensional expansion of cities has become a hot spot in urban research.Chengguan District is the economic,political and cultural center of Lanzhou City and the most central area of Lanzhou City.Affected by the violent contradiction between urban development and river valley terrain,the three-dimensional space of Chengguan District has undergone significant changes.In order to fully understand the urban development characteristics and laws of Chengguan District from a three-dimensional space,this study uses multisource remote sensing images,topographic maps and open source network data as the basis,and uses visual interpretation and a two-dimensional map-based city 3D information extraction method to obtain The boundary data and three-dimensional vector data of buildings in the Chengguan District during the typical period from 1975 to 2018(1975,1987,1998,2007 and 2018).On this basis,using mathematical statistics,spatiotemporal process analysis and autocorrelation analysis methods,the spatiotemporal changes and driving factors of the three-dimensional characteristics of Chengguan District were analyzed from the horizontal direction,the vertical direction of the terrain level and the vertical direction of the building level and get the following conclusion:(1)From the perspective of two-dimensional space,the shape of the built-up area tends to be compact and regular,and the area increases year by year.The northeast direction is the main direction of urban development.During the study period,the area of the built-up area continued to expand,and its horizontal growth rate and intensity continued to rise before 2007,but slowed down after 2007.The northeast direction is the main direction of urban development,followed by the northwest direction.The shape of the built-up area tends to be compact and regular,but since 1987,its rate of change has gradually slowed down.(2)From the perspective of terrain,the layout of the city first tends to low-relief areas,then high-relief areas.The low-lying areas within the urban river valley are larger and the terrain is relatively flat.The closer to the edge of the valley,the more complex the terrain.The city expands downwards and then upwards along the direction of the terrain.As the developable area of the flat area decreases,the built-up area of the higher terrace / slope and undulation area increases significantly.In different elevation ranges and slope ranges,obvious downward “downhill” and upward “uphill” expansions occurred,and the maximum elevation and slope ranges reached by building distribution increased significantly.(3)From the architectural perspective,the structure of the building has changed significantly,the spatial distribution of the three-dimensional features is significantly different,and the expansion modes are different in different periods.Specifically,with the passage of time,the scale of multi-story buildings has risen,the proportion of multistory buildings has gradually declined,and the proportion of other higher-type buildings has increased.And the growth rate of high-rise buildings is faster than that of middle and high-rise buildings.The three-dimensional features such as building height,coverage and floor area ratio vary with the time of regional development and construction,and there are obvious differences in spatial distribution.Horizontal expansion and vertical expansion dominated the urban development before and after 2007,respectively.(4)The use of three-dimensional space in urban development has become more efficient.The skyline of Chengguan District has undergone a morphological change from a low building height and a relatively flat distribution to a high building height and a relatively flat distribution,with extreme values appearing in some areas.The average height of urban buildings has obvious spatial agglomeration characteristics.The "high value-high value agglomeration" area changes from the old city to other areas,while the location of the "low value-low value agglomeration" area does not change much.(5)National policy is the leading force to promote the development of Chengguan District.Population growth and economic growth are the internal driving forces of urban development.The terrain of the river valley restricts the horizontal expansion of the city while accelerating the process of vertical expansion of the city,and at the same time,promotes the development of the city divided into different region.In addition,using three-dimensional urban expansion to measure urban development has obvious advantages over two-dimensional urban expansion.