Ron Russell wrote: > > I always thought > > http://www.ordnancesurvey.co.uk/oswebsite/gps/information/coordinatesystemsi > nfo/guidecontents/index.html > > was a good description, at my sort of level. thanks, link added to the wiki page, http://grass.gdf-hannover.de/wiki/Gis_Concepts#Background_material Hamish