Has the Maritime Silk Road Initiative promoted the development and expansion of port city clusters along its route?

Over the past decade, rapid urbanization and significant regional population migration have led to profound changes in the urban geography along the Maritime Silk Road (MSR) route. However, current research still lacks quantitative investigations into urban development under the backdrop of the MSR initiative, as well as discussions on the mechanisms and policy effects of the MSR initiative on regional urban development as a whole. Drawing upon theories and methodologies from various disciplines such as urban geography, urban economics, and political geography, this study quantifies the development changes of MSR port city clusters (PCCs) at different research scales. From 2000 to 2020, PCCs along the MSR route have all exhibited positive expansion, with an average annual growth rate of 5.2 %, accompanied by a rapid increase in NTL values. Rapid urbanization exhibits significant regional disparities, with Southeast Asian PCCs gradually emerging as hotspots for urban expansion, and the NTL centroid rapidly shifting southeastward at a speed of 27 km/year. Spatial change analysis results effectively demonstrate the temporal and spatial alignment between urban development and the MSR initiative. Some newly established small cities are emerging along the MSR route and have the potential to become new locations for rapid urbanization. DID models were constructed to illustrate the positive role of the MSR in driving urban expansion and development, with population, port connectivity, and Chinese investment playing significant roles. Furthermore, this study emphasizes the importance of selecting the appropriate research scale for studying urban development under policy influences. The choice of urban scale must maximize the representation of policy or planning characteristics, with studies at the PCC scale being more representative of the MSR initiative compared to national-scale studies. This study provides new insights into the development changes of port cities at different scales along the MSR initiative and sheds light on the selection of research scales for urban issues under policy influences.