To use them you may need to deselect the preinstalled maps and I'm not sure how that's done on the c340.On a Nuvi it's just a matter of tapping a checkbox in a list of available maps.I believe the C340 has it's maps preinstalled on the device.If so, you can place other maps on an SD card and they would not effect the preinstalled maps.Term "routable map" means that device can trace route form point A to point B but ONLY IF device supports this function.Some older off-road handheld devices don't have routing option, but if they can read map format you still can use this maps with them.And if you are loading maps that overlap with coverage you can have problems with routing.
Coverage can differ sometimes, as often there are non commercial projects created by users. I already knew about those methods, but unless you know ahead of time the link will take you off site the easiest way is to just left click the link.Garmin has not yet incorporated NAVTEQ's updates for that area.At 3.5GB for just the United States, I have to wonder what it has versus the Garmin maps which are considerably smaller and include all of North America.Other option is to reload new map witch will cover all area that is need. If you use any of this maps share on this topic details.Like which maps were you using and in what region, how accurate they were, how well routing worked and possible problems you had.
Since it doesn't matter how old the map is to alert for RLC it is always in the car and comes on with the ignition switch.