David O'Sullivan Alastair Morrison John Shearer Using desktop GIS for the investigation of accessibility by public transport: an isochrone approach. 85-104 2000 14 International Journal of Geographical Information Science 1 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=1365-8816&volume=14&issue=1&spage=85 db/journals/gis/gis14.html#OSullivanMS00