Linking G2SFCA method and circuit theory to promote spatial equity and landscape connectivity in urban ecological infrastructure

Protecting and constructing urban ecological infrastructure (UEI) is an important spatial means of improving the quality of life of urban residents, enhancing the benefits of the urban environment, and improving urban habitats. Landscape connectivity is the basis for UEI to play an ecological role. Spatial equity is an important goal for UEI to enhance urban resident happiness and sense of access and achieve environmental justice. Taking Yantai city as an example, this study analyzed the UEI morphological spatial pattern based on morphological spatial pattern analysis and calculated the spatial accessibility of UEI based on the gravity -based two-step-floating catchment area (G2SFCA) method. In addition, the study proposed the concept of accessible UEI and reflected the spatial differences in the equity of accessible UEI in urban residential areas through equity modeling that was oriented to connectivity enhancement and equity improvement. Moreover, the study integrated the locationallocation model and circuit theory to optimize the spatial layout of the existing UEI and construct an urban ecological corridor that considered landscape connectivity and leisure and recreational convenience. The results of this study showed that the proportion of bridge and island areas with connecting functions in the existing UEI in Yantai was only 10%, and they had not yet formed a complete network structure; hence, connectivity improvements were needed. In addition, the equity of accessible UEI in the residential areas of Yantai was generally good, and more than two-thirds of residents had sufficient access to UEI. However, approximately 32.7% of the residents in the four old city areas lacked a UEI distribution within their effective commuting time. Moreover, UEI layout optimization could improve the equity of accessible UEI in residential areas; however, the method of adding a new UEI was not applicable to areas with high concentrations of urban populations and stable urban spatial layouts. Furthermore, urban ecological corridors could effectively improve the connectivity and equity of UEI; however, 70% relied on existing road systems and needed to enhance their ecological attributes. The UEI equity of residential areas was highly correlated with house prices, indicating an obvious spatial injustice in the UEI layout in Yantai. Planners and governments should promote urban environmental justice through effective conservation and construction measures by incorporating established ecological and artificial infrastructures into UEI planning to achieve equitable access to UEI services for urban residents. This study provides a spatial reference and methodological support to enhance the equity and connectivity of UEI.