A friend of mine has a bike sat nav . Which has a Green Lane map system . He does a lot of off-road trails riding. Over here we have a lot of footpath/bridle-paths (mainly for horse riding) This bit of kit has all the path's on it so you can go off road following the map for miles and brings you back onto main roads . Found link to a small post about it showing a photo. Would have thought there are similar systems over your way. Might be worth checking land-rover/off-road clubs sites as I think more people do this in cars than bikes . One good thing about having one is if you get into trouble .You can get help alot quicker to you as you Know exactly where you are.
http://greenlanecrew.proboards.com/index...2398&page=1The sat nav
http://www.tredz.co.uk/.Memory%20Map-Adventure-3500-Handheld-GPS-Unit-Great-Britain_40729.htmBut I think you have to have something like this which you pay monthly/yearly
http://www.trailzilla.com/ Have put in canda for you . but does all over the world . Give's you something to check out keith and give you bit more understanding maybe.
Atb geoff