There is a serious bug that breaks routable maps when --route is NOT given. This bug will in future break routing on most GPS devices and is already inflicting Mapsource 6.16.1 and Basecamp 3. This means that also if you compile maps that are not routable, you have to pass the --route parameter. Else the GPS / Mapsource looks into an empty NOD table and may crash. This will happen as soon as you mix routable maps with the non routable mkgmap created maps. The problem is that Mapsource and the GPS search for 63440000.NOD data (63440000 as an example placeholder for the mapname). "Falagar", a developer at Garmin said to release a fix for this bug in Mapsource 6.16.2 however mentioned that this fix will not be carried on to GPS devices and will still mean a deterioration of overall routing. I'm not sure what the exact problem for this is (I just tried even very old mkgmap versions like 858 and also there the problem arises) but currently this means that --route should be the compulsory for all map creation, also not routable ones. If you have old maps (eg transparent contourline maps) that are troublesome to rebuilt, then opening with gpsmapedit, saving as mp and recompiling passing --route parameter is enough to solve the problem. I think that until the bug is found, mkgmap should adopt --route as standard, because it may happen that if users put an mkgmap created without --route onto their GPS besides other routable maps, these maps might impact autorouting for the other routable maps (except if "deactivated" on the GPS).