Multilevel“city-firm”networks in the Yangtze River Delta and its formation mechanism: A study based on the ML-ERGM model

The increasingly important intercity elements flow and the unique urban administrative system in China lead to regional organizations such as urban agglomerations possessing both networked and hierarchical characteristics. Taking the Yangtze River Delta urban agglomeration as an example, this study comprehensively considered spatial continuity, connectivity, and the evolution of the Yangtze River Delta's integration trend to divide the region into the central layer and the peripheral layer. Using a multi-level exponential random graph model (ML-ERGM), it dissected the coexistence of the network and hierarchical structures in the Yangtze River Delta urban agglomeration network from the perspective of business connections. It also examined the formation mechanism of this pattern from the structural aspects of basic structural effects and complex structural effects, as well as external factors such as urban economic scale, intercity transportation accessibility, intercity physical distance, and administrative boundary effects. The research findings are as follows: 1) The intercity connection network of the Yangtze River Delta urban agglomeration exhibits an overall hierarchical structure and shows a noticeable "capital attraction effect" in terms of intercity connection strength. 2) The intercity connection network in the Yangtze River Delta is significantly driven by structural effects, with specific dynamics including the closure of the central layer, the transmission in the peripheral layer, and interlayer expansion. 3) Urban economic scale is an important influencing factor on the intercity connection network. In addition, a convenient transportation network, close geographical distances, and being located within the same province can all promote intercity business connections, but their effects on different layers of the network are heterogeneous. The results of this research can provide some scientific support for the optimized development of the Yangtze River Delta intercity connection network.