Coupling Coordination Degree and Influencing Mechanisms of Virtual-Physical Vitality in Urban Space: A Case Study from Changsha, China

In the digital economy era, Urban vitality has transitioned into an intertwined Virtual-Physical system. This study examines Changsha’s five urban districts through a dual-dimensional framework bridging physical (social, economic, cultural, and ecological) and virtual (video, social, and digital life) dimensions. Integrating Coupling Coordination Degree (CCD) and XGBoost-SHAP models, we elucidate the spatial patterns and nonlinear drivers of Virtual-Physical synergy. The results indicate that: (1) Urban Vitality exhibits a significant center-periphery gradient. Although the Coupling Degree between the two dimensions is high, the overall CCD remains relatively low, reflecting pervasive spatial mismatches. Notably, 55 units display a reverse pattern where Virtual Vitality surpasses Physical Vitality, suggesting that digital flows can reconfigure urban space by transcending traditional locational constraints. (2) Interactions within the built environment exert pronounced threshold effects. Structural elements require specific critical masses to activate synergy, beyond which marginal returns diminish, as exemplified by the U-shaped effect of the Green View Index and the inverted U-shaped effect of Spatial Enclosure on CCD. (3) Interaction analysis identifies building density as a multiplier, unlocking the synergistic potential of land-use mix and transport networks once critical thresholds are surpassed. Furthermore, the efficacy of population and transit relies on dense road networks and intersection, while functional diversity buffers against negative micro-environmental impacts. This study advocates for a shift from facility-increment to threshold-triggered precision strategies in urban regeneration, providing empirical support for human-centric planning in the digital twin era.