Spatial data and intelligence Second International Conference, SpatialDI 2021, Hangzhou, China, April 22-24, 2021 : proceedings - Pan, Gang; Lin, Hui; Meng, Xiaofeng 1964-; Gao, Yunjun; Li, Yong; Guan, Qingfeng; Ding, Zhiming (Information systems and applications, incl. internet/web, and HCI, 2021)