Does every public open space (POS) contribute to sustainable city development? An assessment of inefficient POS in Beijing

Public open space (POS) plays a crucial role in influencing the urban environment, ecology, public health, and economic vitality. However, not every POS is being efficiently utilized, while the inefficient POSs occupy large areas and can negatively affect socio-economic development, thus posing a threat to sustainable city development. Existing studies evaluate POSs solely based on benefit outcomes, but ignore POS functional types and contextual environments. To address this issue, a categorized, integrated, and relative evaluation method, i.e., utilization efficiency (UE), is proposed to identify inefficient POSs, where essentially measures the ratio from benefit outcome to resource occupation of each POS. We firstly classify POSs into five types by considering their core functions, then measure their UEs to extract efficient and inefficient POS, and finally visualize key causes of different types of POS. Our results reveal 3,138 inefficient out of 10,943 POSs in Beijing, and show the inefficient POSs that are concentrated in the southern Beijing and northern regions between the 5th and 6th ring roads, mainly affected by local population density and environmental resource. Drawing on the features of inefficient POSs, it is suggested to increase small green spaces and sky gardens in the downtown areas, improve service facilities and basic tourism infrastructure in the suburbs. Accordingly, this study firstly incorporates POS functional types and resource occupation into the utilization efficiency evaluation, providing spatial optimization recommendations of POSs to facilitate sustainable city development.