So compared to my near-annual rant about updating my Zumo 660 with the latest European maps, this was ridiculously easy.
Turns out OpenStreetMap fully supports Garmin GPSs these days and it’s a simple matter of downloading and installing the map(s) that you want.
Of course, the maps aren’t commercial quality, there’s no 3D buildings, but they work and allow routing both within MapSource and on the GPS itself and come with a plethora of waypoints etc. Best of all, being open source, if you find any errors or omissions in the map data you can submit the fixes yourself and they’ll be available to everyone shortly.
Not just limited to Japan either, grab your free maps from here : http://garmin.openstreetmap.nl/