Messages

QGis comes with the osgeo4w shell  which implements GDAL.  It's command line but if you need the Clark 1866 ellipsoid for instance this is the app for you

Newer versions of gpsmapedit (maybe > 2 ) can use MapTk which is still under active development.  I have no personal connections with this software or it's author but I have a soft spot for it because it generated the first img file I was able to see in basecamp.  YMMV

I've never used cgpsMapper, only MapTk and the recommendation for that is map sizes should be kept to ~15 Mb.  Looking at an old gpsmapsupp file from mapsource it was made up of multiple maps corresponding to 7.5 minute USGS quads.  When compiling maps I've edited I get an img file per map.  Converting to GMAP format to enable adding to basecamp each individual image is added as a map tile (I believe, I'm certainly no expert and welcome correction if this is wrong) Viewing is seamless in basecamp so I *believe* the smaller map tiles are handled by the Garmin software.  In this manner I've been able to make maps consisting of multiple GB of .mp files.

The MapTk documentation is pretty comprehensive but only covers the compiling portion, not the map authoring portion.  BTW opening individual maps from the gpsmapsupp file wasn't a problem,  so much so in fact I've forgotten the specifics.

In case anyone else is using cgpsmapper to do this,  the easiest way I've found is to open the properties tab for the road of interest and the type of container (shield, square, round, etc ...) can be chosen from a drop down menu.  For multi section road there is a last button which will automatically fill in the last name and container used.