Other question according to the Mapsoruce Flag (Ms=1 or Ms=0).
When You use this method to see a map from the openstreetmap-community (velomap, openmtbmap, openfietsmap etc.) and You change the Ms(=0) you can see the map in Basecamp which is on gps or sd-card (connected to PC). So Far So good.
But in Basecamp is also a Global Application Basemap (v2 for the latest Basecamp 3.2.2.). It looks like the gmapsupp.img is transparant because You see the Basemap together with Your gmapsupp.img. (example: You see the highways double). Gmapsupp.img from Garmin (created with MPC ?) don't have this.
You can change the transparency of the osm-gmapsupp.img, but that has no effect. Osm-maps are normally made whith Mkgmap. Maybe that's the problem but maybe also the solution.
Somebody recognize this "problem" and have the solution/answer the solve this or can give a parameter which is maybe wrong in a gmapsupp.img (and can be changed by Gmaptool).
@Edit : latest version of Mkgmap (30/11/2011) should solved this problem. Just wait now for the new maps with this version.