“…Other projects aim at improving spatial indexation, spatial aggregation or spatial operators (e.g. Gupta, Harinarayan, Rajaraman & Ullman, 1997;Han et al, 1998;Papadias, Kalnis, Zhang & Tao, 2001;Prasher & Zhou, 2004;Stefanovic et al, 2000;Wang, Pan, Ren, Cui, Ding & Perrizo, 2003;Zhang, Li, Rao, Yu, Chen & Liu, 2003;Zhou, Truffet & Han, 1999).…”