Only discovered this during the week - Openstreetmap have a free service to bundle-up OSM maps of anywhere in the world for Gamin users - you select country, then click on the areas you want or don't want - then request the files.
Half an hour later, their server bundles up a file that can be copied to your Garmin, *and* a useful program that will install the OSM maps onto Garmin Training Centre (Windows or Mac)
So instead of seeing your route on the rubbish "global map", you see it on a real, detailed map.
http://garmin.openstreetmap.nl/ is the place to go to :)
Seems to cover the entire globe, except for a patch of the India Ocean