Using an improved 3SFCA method to assess inequities associated with multimodal accessibility to green spaces based on mismatches between supply and demand in the metropolitan of Shanghai, China

•Urban green space accessibility (UGSA) in Shanghai showed inequity and spatial disparity.•Old towns generally had more equal UGSA than built-up districts.•The population demand index showed that UGSA needed to improve in central city areas.•Population variables results were different from the population demand index results.•Higher speed travel promoted more equal UGSA in Shanghai.