Identifying plot patterns and formulating morphological control strategies in a mountainous historic urban area: a case study of Chongqing

Urban morphology has long recognized plot patterns as fundamental units shaping urban form and supporting heritage-sensitive regeneration. Yet, existing plot-based studies largely focus on flatland contexts, leaving mountainous historic cities—where steep terrain fundamentally constrains land subdivision and development logic—insufficiently examined. This study adapts established morphometric approaches to mountainous historic urban areas by integrating K-means clustering with a multi-scale typo-morphological framework. Using the Yuzhong Peninsula in Chongqing as a representative case, 688 plots were analyzed based on four geometric indicators: plot area, frontage, compactness, and slope. Six plot types and five dominant plot pattern categories were identified. Rather than tracing diachronic evolution, the study examines the contemporary spatial distribution of plot patterns and interprets their differentiation through a temporal–institutional lens. The results reveal pronounced east–west differentiation, center–periphery layering within the former walled city, and ring-road-related pattern transitions in the western area, reflecting the combined effects of topography, land tenure, urban policy, and construction modes. Building on these findings, the study synthesizes the morphological specificity of mountainous historic cities, characterized by topography-responsive plot forms, terrain-driven consolidation, and three-dimensional spatial organization. It further proposes a plot-pattern-based, multi-tiered morphological control approach to support organic regeneration while preserving historic urban character. This research contributes a slope-sensitive analytical framework and offers transferable insights for managing regeneration in topographically complex historic cities.