[1] George Mason Univ, NSF Spatiotemporal Innovat Ctr, Fairfax, VA 22030 USA
[2] George Mason Univ, Dept Geog & GeoInformat Sci, Fairfax, VA 22030 USA
[3] Univ Calif Santa Barbara, Dept Geog, Santa Barbara, CA 93106 USA
[4] Univ Minnesota, Dept Comp Sci, Minneapolis, MN 55455 USA
[5] Wuhan Univ, Shanghai, Peoples R China
[6] Z Ventures Grp, Shanghai, Peoples R China