Abstract
The development of cities in the vertical dimension is important in valley-type cities where physical growth is limited by terrain. However, little research has focused on three-dimensional urban expansion of valley-type cities. Lanzhou is a typical valley-type city in China and Chengguan District is the core area of Lanzhou City. This research is aimed at understanding the development of valley-type cities through the analysis of the three-dimensional urban expansion of Lanzhou Chengguan District and providing a reference for urban planning. We extracted five periods of architectural contours and height information between 1975 to 2018 with the support of multi-source remote sensing and network data. We used overlay analysis and mathematical statistical methods to analyze urban horizontal expansion and used the building density, floor area ratio, vertical expansion speed, fluctuation degree, and skyline to analyze urban vertical expansion. We found that the mode of horizontal expansion of Chengguan District shifted from adjacency to enclave through mountain area reclamation. The area with the fastest vertical expansion speed first appeared in the horizontal expansion completed area, and then in both the rapid horizontal expansion area and in the horizontal expansion completed area. Before 2007, the speed of horizontal expansion increased and reached its peak while the vertical expansion speed was relatively stable. After that, the former decreased, and the vertical expansion increased rapidly and dominated the urban development. The vertical expansion of the valley-type city gradually dominates urban development. Urban planning should consider the three-dimensional expansion, especially in the vertical dimension.
Highlights
IntroductionUrban sprawl tended to encroach on suburban in horizontal direction [2], under the pressure of rapid population growth, with many negative effects on society and the environment [3,4], such as biodiversity loss [5], air pollution [6], and urban heat islands [7,8]
Cities are where humans have the strongest effect on the natural environment [1]
The results show that the horizontal expansion of Chengguan District was mainly along the original floodplain in the northeast direction, principally by adjacency expansion
Summary
Urban sprawl tended to encroach on suburban in horizontal direction [2], under the pressure of rapid population growth, with many negative effects on society and the environment [3,4], such as biodiversity loss [5], air pollution [6], and urban heat islands [7,8]. Growing cities are gradually improving land use efficiency with increasing building height in vertically to control urban outward sprawl [9]. It is more common in Asian countries with high population density to build many middle- and high-rise buildings [10]. An in-depth understanding of the process of urban time-space expansion and change in three-dimension (both in horizontal and vertical direction) is fundamental for rational planning and efficient use of urban space to sustainable development [14]
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