The delineation and effects of urban development boundaries under ecological constraints: The case of urban Nanjing, China

• Various models were adopted to delineate UDBs under ecological constraints. • Multi-source data were integrated to support model simulation. • The delineated UDBs had a high consistency with the proposed urban layout. • Ecological constraints should be considered in determining eco-friendly UDBs. The delineation of urban development boundaries (UDBs) is an essential part of spatial planning and a powerful tool for implementing spatial governance. With the central city of Nanjing as an example, we used various models, including the logistic regression analysis model, InVEST model, and cellular automaton (CA) model, to evaluate the ecological importance, simulate the spatial expansion of construction land, and delineate the UDBs of various urban spatial units under ecological constraints, and determine the eco-environmental effects of the obtained UDBs. The results revealed that the important ecological lands, which were mostly woodlands, covered 422.05 km 2 and acted as the ecological bottom line for regional sustainable development. The simulated UDBs under ecological constraints considered the dual demands of urban spatial expansion and a high-quality eco-environment; they effectively prevented urban expansion from occupying important ecological lands and destroying regional eco-environmental quality. The obtained UDBs were highly consistent with the proposed urban layout of local governments, and our simulated results of the UDBs could provide differentiated development orientations from the perspective of land use protection and development. Finally, we noted that urban expansion is dynamic, complex, and systematic and is also affected by the interaction of multiple factors, and the constraint of ecological importance should be emphasized to coordinate the relationship between land development and ecological protection.