Nonlinearity and Scale Effects: How the Built Environment Modulates Urban Vitality in Multi-Scale Community Life Circles Across Weekdays and Weekends

Boosting urban vitality (UV) in residential living spaces has become a core component of advancing the people-centered urbanization strategy. However, previous research has mainly focused on exploring UV at the scales of streets, blocks, and grids, with few nonlinear explorations conducted across different temporal dimensions at the scale of residents’ daily life. Therefore, this article adopts the XGBoost-SHAP model to explore the nonlinear and interaction effects of a built environment (BE) on UV across multi-scale community life circles (CLC), distinguishing between daytime and nighttime on weekdays and weekends. The results indicate that UV on weekends is higher than on weekdays, except for 5 min CLC (5MCLC). UV is highest in 10 min CLC (10MCLC) and lowest in 5MCLC. The mean building height (MBH) and Normalized Difference Vegetation Index (NDVI) have always been the most important indicators affecting UV. Unlike previous studies, the green view index (GVI) and sky view factor (SVF) are negatively associated with UV. The nonlinear relationship between BE and UV on weekdays exhibits greater regularity. The effects of other BE indicators on UV exhibits spatiotemporal heterogeneity, with the relative influence changes in commercial accessibility (CA), distance to metro (DSM) and distance to bus (DSB) being the most significant. The nonlinear and threshold effects of BE on UV show significant changes, except for GVI, SVF, and NDVI, at different times and scales. The threshold for cultural and leisure accessibility (CLA) is higher on weekdays than on weekends, whereas that for DSM is higher on weekends than on weekdays. The interaction effects between the building density (BD) and MBH, park and square accessibility (PSA), and DSM is significant at different scales. This study will provide a scientific basis for optimizing BE and differentiated planning of CLC, which further contributes to enhancing UV and promoting urban sustainable development.