Elaborating non-linear associations and synergies of subway access and land uses with urban vitality in Shenzhen

Previous studies on the built environment and urban vitality often assume that they follow a pre-defined (mostly linear in parameters) relationship, and few studies substantiate whether high-quality transit (T) and supportive land development (D) are synergistic to vibrant urban places. This study employs gradient boosting decision trees to examine the irregularly non-linear associations between the built environment and urban vitality, using Shenzhen as the case study and the Baidu Heat Index as a proxy for vitality. It reveals that their associations change drastically past some thresholds of built environment attributes, and that there are non-linear synergies between T and D. The findings provide guidance for neighborhood planning and have implications for cities that seek transit investments and transit-oriented development.