Juan Touriño Jorge Parapar Ramon Doallo Marcos Boullón Francisco F. Rivera Javier D. Bruguera Xesús P. González Rafael Crecente Carlos Álvarez 377-396 2003 17 International Journal of Geographical Information Science 4 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=1365-8816&volume=17&issue=4&spage=377 db/journals/gis/gis17.html#TourinoPDBRBGCA03