if these are the ones with the flick lock closing i really rate them. i havebeen using them for a number of years now with no problem. i use them in the lake district, peak district and the pyrenees. thy take my 13 stone weight whenvaulting swollen streams with no trouble
when you have the map page showing press the "menu" button which should bring up a menu of 3 items. select "set map". This should bring up a longer menu, scroll down to "map information select map" this should show the maps available on your unit and you can now disabe the base map.