Exploring the spatio-temporal characteristics and driving factors of urban expansion in Xi'an during 1930–2014

Analyzing and understanding the spatial and temporal dynamics and the driving factors of urban expansion over time is crucial for providing solutions to address social, economic and ecological problems caused by urbanisation. Previous studies generally relied on remote sensing data and examined the process of urban expansion in relatively shorter time periods. Taking Xi'an as the case study, this paper uses the proposed urban boundary extraction method by integrating multi-source data to analyze the spatio-temporal characteristics of long-term urban expansion. The research focuses on indicators including expansion intensity, expansion direction, city centre of gravity, compactness, and elasticity, and identify and discusses the driving factors of urban expansion. The results show that the urban expansion of Xi'an has undergone two cyclical changes during 1930-2014. The urban form presents a 'horizontal rectangle-inverted triangle-concave' evolution feature. The city centre of gravity shifts to the northwest. The compactness continues to decline, and the elasticity coefficient rise. It has been identified that economic and demographic factors together with the industrial structure have driven urban expansion, and urban planning policies has influenced the directions of the expansion. The conservation of great ruins in Xi'an has affected the evolution of its urban morphology. Based on the results, we further discuss the future expansion directions of the city, and provide specific suggestions for future urban planning in order to better coordinate urban expansion, and at the same time provide adequate protection to large heritage sites and support urban sustainability. These findings provide not only valuable insights about urban planning of Xi'an, the methodological approach developed in this research is also applicable to other historic cities with similar characteristics in China and beyond.