USING A GARMIN CAR GPS WITH OTHER TYPES OF MAPS

Yes, the most useful may be these:

http://wiki.openstreetmap.org/wiki/OSM_Map_On_Garmin/Downloa...

although there are also other sites with map, including topo maps.

I've not installed or used the OSM maps but someone will surely pipe in with more help soon. The nice part of the OSM maps is that like the genuine Garmin maps, routes can be created with them.

I used the OSM maps for our trip to the Caribbean and they worked well.

I download topographic maps to my Garmin as an additional source of information. I find it useful, particularly when travelling in mountainous areas.

GPS File Depot.com is an excellent source for these maps which are free to download. Donations however are accepted.

http://www.gpsfiledepot.com/

I've used the Colorado Topo maps from GPS file depot many times for 4-wheeling in the Colorado San Juan Mts. Most are VERY good.

Make sure your GPS has a large enough SD card installed and you can switch back and forth between the Garmin map and the Topos.

I have use OSM maps during trips to Spain, Australia and England and they worked well in my Garmin GPS

I just like to say, that other maps (especially free types) can have limited coverage or less to none perks (like POI). I'm not saying that they are bad, but be aware about possible limitations you can encounter. We had some members complaining that those free maps had those "problems". On other hand, in some places free maps can be more detailed than commercial maps, and often are updated much faster and more accurately than maps supplied by Garmin.

While the Caribbean maps I downloaded had POIs, you couldn't route to addresses, only to places you select on the map or to POIs. This was only a minor inconvenience in the Caribbean, but I can see that being more of an issue in larger or more densely populated countries.