The impact of city walls on urban expansion and structure of small historical cities: a Space Syntax analysis of Zhengding, China

This study employs Space Syntax analysis to examine the urban expansion of Zhengding, a small historical city in northern China. Focusing on the impact of the city walls on urban form, spatial connectivity, and functional distribution, the research analyzes the city’s growth at four key stages (1966, 1992, 2008, and 2024). The findings reveal a complex and evolving impact by the city walls, beyond that of a simple constraint. First, the walls mediated a unique “overflow before filled” expansion pattern, where partial demolitions guided expansion outward before the inner city was fully developed. Second, contradicting existing research, the city’s Axial Synergy increased over time, revealing the walls’ previously unappreciated function as a “stabilizer”. Finally, the walls’ impact is highly differentiated, creating divergent development logics inside and outside the city, as evidenced by the varying correlation between syntactic measurements and the distribution of commercial POIs. This study offers a refined methodological framework for analyzing the spatial structure of small historical cities and the impact of physical boundaries, providing insights for planning and heritage preservation policy, particularly on balancing development and heritage preservation.