Decoding Spatial Vitality in Historic Districts: A Grey Relational Analysis of Multidimensional Built Environment Factors in Shanghai’s Zhangyuan

Enhancing the vitality of historic districts is a key challenge in China’s urban regeneration. This study takes Shanghai’s Zhangyuan Historic District as a case, constructing a framework with six spatial indicators—width-to-height ratio (W/H), interface transparency, connectivity, integration, Universal Thermal Climate Index (UTCI), and mean radiant temperature (MRT)—across spatial morphology, path accessibility, and thermal comfort. Using Grey Relational Analysis, the study quantitatively examines how these factors affect spatial vitality and pedestrian behavior. Findings indicate that, overall, W/H and connectivity are the primary drivers of vitality in plazas and alleys, while thermal comfort (MRT, UTCI) strongly affects stationary behaviors. By typology, plazas exhibit the strongest association with interface transparency (grey relational grade = 0.870), demonstrating that open sightlines and permeable interfaces promote pedestrian flow and staying. North–south alleys show pronounced associations with thermal comfort (MRT = 0.918; UTCI = 0.874), suggesting microclimate-friendly environments can substantially enhance vitality in linear walking spaces. East–west alleys are dominated by connectivity (0.831) and W/H (0.849), whereas integration shows a low grade (0.512), revealing weaker configurational coherence for this spatial type. At the micro-scale, connectivity outperforms integration in predicting pedestrian route choices, reflecting actual movement preferences. The study highlights the combined effects of multidimensional built environment factors and provides a scientific basis for targeted spatial optimization, sustainable renewal, and vitality-oriented design in historic urban areas.