Spatio-temporal evolution of urban built-up areas and analysis of driving factors —A comparison of typical cities in north and south China

Urban expansion is an important manifestation of urbanisation. Based on the impervious surface aggregation density (ISAD) method, this study extracts the urban built-up areas (UBA) range of 12 major cities in the north and south of China from 1995 to 2015. Comprehensive use of the urban centre of gravity, fractal dimension, compactness, urban spatial morphological expansion mode, urban expansion speed, and other indicators was applied to explore the spatio-temporal evolution characteristics of urban expansion. The statistical method GeoDectector (GD) was used to analyse the impact of economic, transportation, natural environment, and social factors on urban expansion. Results show that the 12 cities were shown to have different expansion characteristics and spatio-temporal evolution characteristics. Most northern cities had single-core expansion, while most southern cities had multi-core expansion. Most of the spatial forms of cities tended to be discretized, and the urban expansion process of southern cities was obviously more rapid than that of northern cities. GeoDectector revealed that urban expansion in both the north and south was mainly related to population and economy. Social factors explain the expansion of southern cities, and while the intensity was stronger than that of the northern cities, the natural factors were opposite, and the traffic factors were not significantly different. This analysis confirms the differences in economic development between the north and south of China and provides a scientific reference for the formulation of national-scale urban development policies. In the context of global urbanisation, the results from this study will provide a Chinese sample for understanding the temporal and spatial characteristics of urban expansion, which can serve as a good reference value for other countries and regions worldwide, especially for urbanisation research in developing countries.