Marko Mäkelä wrote:
Another idea: would it be possible to create a global contour line map from the ASTER data and distribute it?
I don't know about ASTER, but with srtm2osm I didn't manage to generate the whole of Europe at once. Germany did work, though.
Could the contour line map be an overlay on a more variable map?
Yes, that's what I have done for my topo map: http://www.kleineisel.de/ralf/gps/garmin/
Would the tile borders have to match?
No, that's not necessary.
Could the two maps (contours and OSM-based overlay) be enabled or disabled from the device's settings menu?
Yes. If you use two different family-IDs, make two complete gmapsupp.img and join them with gmaptool it works.
It would be useful to have a "static" contour line map, because elevation data does not change (or is not surveyed) as often as OpenStreetMap.
Sure, I recycle my SRTM layers when I make an updated OSM layer. I did recreate them a few weeks ago because the "max 4 tiles bug" in mkgmap splitter was fixed.