GBOpen :Great Britain Map for Garmin Mapping devices
Map Comparisons
Here is the same area of Somerset as depicted by four different maps:
GBOpen (in Basecamp) :Map compiled from Open Street Map with added contours (in Basecamp)
crook 1
Ordnance Survey 'Landranger' paper map 1:50000Ordnance Survey 'Explorer' paper map 1:25,000
Crook Peak on the Mendips is quite popular with walkers and, therefore, with Open Street Mappers. Go to somewhere less popular such as this area on the England/Wales border near Knighton and the advantages of the comprehensive OS mapping are clear:
GBOpenStow hillStow Hill GBOpenStow Hill OSMStow Hill OSM

A peak in North Wales as displayed on an Etrex.
       On the left is GBOpen, on the right is Garmin UK Topo Lite

Yr Elen GBOpen               Yr Elen Garmin