Benjamin E. Teitler Michael D. Lieberman Daniele Panozzo Jagan Sankaranarayanan Hanan Samet Jon Sperling 18 2008 GIS http://doi.acm.org/10.1145/1463434.1463458 conf/gis/2008 db/conf/gis/gis2008.html#TeitlerLPSSS08