Quantifying Spatial Openness and Visual Perception in Historic Urban Environments

With accelerating urbanization, the preservation and adaptive renewal of historic urban environments have emerged as critical challenges in the field of urban science. Among various morphological attributes, spatial openness plays a fundamental role in shaping visual perception and influencing human well-being, but remains insufficiently examined within the context of historic streetscapes. This study investigates the spatial configuration of Tangchang Ancient Town in Chengdu, China, to elucidate the relationship between spatial openness and perceptual responses. A mixed-methods approach was employed, integrating semantic differential (SD) surveys with a suite of spatial analysis techniques, including GIS-based viewshed analysis, depth-to-height ratios, building density, and street curvature metrics. The empirical findings reveal that increased spatial openness is positively associated with visual comfort, while reduced openness contributes to a heightened sense of enclosure and psychological stress. Mediating factors, such as sky visibility and natural lighting conditions, were identified as significant, with elevation angle and curvature further enriching the explanatory framework. Drawing on these insights, this study proposes a set of context-sensitive spatial design strategies tailored to varying degrees of openness. These include enhancing vertical openness through building form regulation, improving lighting and sky access, integrating vegetation more effectively, and activating corner spaces to support spatial legibility and visual interest. This research contributes to the growing discourse on evidence-based urban design by linking quantifiable spatial parameters with perceptual and affective outcomes. The proposed framework offers practical guidance for the sustainable conservation and transformation of historic urban areas undergoing contemporary urbanization pressures.