Factors influencing China's E-commerce express logistics network: An optimal multivariate-stratification geographical detector model approach

China's rapidly expanding e-commerce express logistics sector has significantly reshaped urban spatial structures and regional economic integration. However, existing studies lack regional comparative analyses and quantitative investigations of key influencing factors, limiting effective logistics network planning, hub allocation, and sustainable development strategies. This study uses big data from China's Smart Logistics Network to construct an e-commerce express logistics (ECEL) network. Using complex network analysis and an optimal multivariate-stratification geographical detector (OMGD) model, this study identifies key influencing factors and elucidates the formation mechanisms of the network. The results revealed that the ECEL network possesses a dual-structure characteristic. Specifically, the nationwide network shows a hierarchical diffusion effect, whereas regional networks exhibit a central diffusion effect. The ECEL network has a distinct hierarchical, diamond-shaped structure, with Beijing, Shanghai, Guangzhou, and Chongqing as core hubs. Network nodes are classified into three tiers: core dispatch, secondary transit, and peripheral-dependent nodes. Regionally, East, West, and South China exhibit a single-core network structure, where intercity ECEL flows follow a Pareto distribution shaped by the industrial development foundation and consumption scale. Central and Southwest China feature a dual-core structure that is significantly influenced by logistics hub planning and infrastructure investments. By contrast, North China and Northeast China adopt a multi-core structure, with intercity logistics flows conforming to a lognormal distribution. Notably, in contrast to other regions, population size is the primary determinant of network structure in these regions. These findings enrich the “space of flows” theory and offer policy guidance for the hub layout and region-specific strategies in China's express logistics system.