Planning vs Market-led? Identifying urban-suburbs transition zones in metropolitan expansion: A multi-source data fusion framework

The rapid urbanization of developing countries has significantly transformed the spatial patterns of metropolitan peripheries. However, the measurement and identification of urban-suburbs interfaces continue to pose considerable challenges, particularly given the wide variability and gap in results obtained using different datasets. To address these issues, this study presents a fusion framework that integrates multi-source urban bigdata, robustly discerning the urban core zones (UCZ) and the urban-suburbs transition zones (USTZ) in metropolitan regions. Further, this framework categorizes types of USTZs based on their modes of expansion. We applied this framework to Chengdu, a rapidly urbanizing megalopolis in Western China, to compare the roles of planning and market forces in metropolitan expansion from 2011 to 2021. The results indicate that over the decade, the area of UCZ increased by 129.19 %, while the USTZs also saw a substantial expansion of 37.10 %. Planning-led USTZ (P-USTZ) accounted for a larger share (62.04 %) than market-led USTZ (M-USTZ) (37.96 %). P-USTZ primarily expanded southward along the arterial roads, exhibiting a more continuous and concentrated spatial pattern, while M-USTZ expanded mainly northward with their spatial pattern being more fragmented and segmented. The spatial development equilibrium among P-USTZ and M-USTZ varied significantly. M-USTZ lagged in urban construction, while P-USTZ experienced intrazonal differentiation, with its southern subregions notably lagging in population agglomeration relative to urban construction. These disparities highlight the spatial disequilibrium driven by planning and market forces in metropolitan expansion, reflecting the complex spatial dislocation between the inner metropolitans and the new metropolitans. The framework adopted in this study effectively identifies the spatial differentiation and disequilibrium arising from government planning and market development in metropolitan expansion, and it underscores the complex interplay between various actors in the spatial production and the shaping of behavior during the urbanization process.