From OpenStreetMap Wiki
This is my My GB Map (GMAPSUPP.IMG file in 7z format). Download using the link (left).
The main features are:
- UK Specific:
- UK colours for roads (Motorways are in blue, trunk roads in green)
- Recognises UK speed limits on the roads
- Public Footpaths are highlighted separately from ordinary footways.
- Speed limits tailored for UK and UK road types. The map doesn't use the default mkgmap speed limits, instead it tailors the speed limits by road type, maxspeed and oneway (to recognise dual-carriageway v single carriageway tagged with national speed limit.
- General purpose map so includes roads, footpaths, most POIs.
- High contrast: it has a white background rather than the garmin default (which is yellow on my etrex).