Just in case any one has a Garmin Edge 520 device, you may be aware the default map is not very useful and the device itself has quite limited memory.
I've created a basemap that covers all of Great Britain (and hence suitable for LEL use) and should leave plenty of space to put the GPX routes on and then record your efforts.
Get it
here on Dropbox.
For information about how it was created
check my OSM diary entry.
As I don't use Garmin Edge 520 device myself, I can't really answer questions about it or what explicitly you need to do with the
gmapsupp.img file.
Hopefully something in the
GPS forum should cover it.
