Sotiris Brakatsoulas Dieter Pfoser Nectaria Tryfona Agnès Voisard Dynamic Travel Time Maps. 255-260 2008 Encyclopedia of GIS http://dx.doi.org/10.1007/978-0-387-35973-1_327 reference/gis/2008 db/reference/gis/gis2008.html#BrakatsoulasPTV08