Unraveling the Impact of Urban Functional Structure on Inter-County Daily Mobility: A Graph Convolutional Network-Based Scenario Simulation for the Greater Bay Area of China

Understanding how urban functional structure shapes inter-county daily mobility at fine scales is essential for sustainable polycentric planning. However, existing origin-destination (OD) models often treat regions as independent observations and lack prior policy evaluation capacity. This study proposes a Graph Convolutional Network (GCN) framework that uses 14 Points of Interest (POI) categories as functional proxies for inter-county daily mobility in 50 counties of the Greater Bay Area, China, drawing on over 6.26 million POI records and county-level mobile signaling OD data. The framework constructs a spatial adjacency graph and learns non-linear mappings between functional profiles and mobility through an encoder–decoder architecture. It achieves a test R2 of 0.766, outperforming gravity, linear, machine-learning, and graph-only baselines. Perturbation-based sensitivity analysis identifies shopping and consumption venues, catering services, corporations and enterprises, and daily life services as the categories most strongly associated with mobility, with rankings stable across perturbation magnitudes and seeds. Scenario simulations reveal heterogeneous, stage-dependent responses. A 10% increase in transport and corporate facilities in Foshan yields a mean response of 6.18%, positive across all 110 county pairs along the mature Guangzhou-Foshan corridor; corporate expansion in the peripheral Guangzhou-Zhaoqing corridor is positive for nearly all county pairs but elicits a smaller mean response; and tourism expansion in the Shenzhen-Zhongshan corridor elicits a weak, near-symmetric negative response. We propose a stage-dependent planning perspective, with mature corridors prioritizing service optimization and job-housing balance and peripheral ones prioritizing capacity investment, and stress that these responses are model-implied diagnostics requiring validation against independent mobility evidence.