Comparing the three-dimensional morphologies of urban buildings along the urban-rural gradients of 91 cities in China

Urban buildings and their three-dimensional (3D) morphologies play important roles in influencing urban climates and the diffusion of air pollutants. Previous studies on the 3D morphologies of urban buildings were mainly conducted within cities due to limited data, and we still lack an understanding of their features among cities, especially along urban-rural gradients. Here, we analyzed the urban-rural gradients of the 3D morphologies of buildings for 91 cities in China by using two groups of morphologic indicators and the concentric buffer method. Then, we used a hierarchical clustering method based on dynamic time warping to classify the gradients. Our results showed that >75 % of grids have a mean height of 9 m to 16 m, and their building coverage ranged from 20 % to 60 %. The gradients of five morphology indicators could be clustered to 9 patterns, and the dominant urban-rural gradient having the average height and building coverage decreasing over distance. This study provided a methodological framework for the quantitative analysis of the urban-rural gradient of the 3D morphologies of urban buildings, and can provide information on mitigate city-scale climate issues.