Downloaded the osm xml file for all France, folded new nodes into ‘array’ of lat and lon doubles, converted osm ways of roads and railways into GMT polylines and passed through GMT to create postscript map. This first attempt is far too finely grained with over 90,000 ways .. the ps file is 6.5Mb which is great for zooming in to look at fine detail, but very slow for the redraw. Need to find some smoothing software. Mapshaper?