Analyzing "economy-society-environment" sustainability from the perspective of urban spatial structure: A case study of the Yangtze River delta urban agglomeration

Sustainable urban development is a common concern of humanity. In order to achieve high-quality urban development, it is imperative to measure cities' sustainability gaps within urban agglomerations and explore the factors affecting sustainability. However, most studies focus on factors at the municipal scale, and the role of intra-urban structure and inter-urban interactions in urban sustainability remains unclear. To address these issues, we analyzed 17 Sustainable Development Goals (SDG) of each city within the Yangtze River Delta Urban Agglomeration (YRDUA), and explored the spatial distribution differences of urban sustainability. In addition, we quantified the impact of urban functional areas, land use, space of flows, geographical location, and climate on "Economy-Society-Environment" (ESE) system by applying the random forest algorithm (RFA)-SHapley Additive exPlanations (SHAP) model. The results show that the eastern YRDUA (coastal area) has outstanding ESE system coordination; the northern YRDUA (heavy industrial area) performs well in economic sustainability but not in the environment; the southwestern YRDUA (high-density forest area) has better environmental performance than its economy and society. Improving transportation facilities and promoting inter-city cooperation are beneficial to economic sustainability; improving social well-being contributes to social sustainability; reducing carbon emissions and protecting urban green areas are crucial for environmental sustainability.