I’ll be getting a Garmin eTrex 3 for Christmas (I currently have an old Edge 2) and I was wondering about the downloadable map feature. Are the maps in a Garmin specific format (Garmin sell the maps themselves) or can I use maps from other sources (such as the ones I’ve bought for TrackLogs)? I was wondering whether it possible to buy digital maps from Ordnance Survery to use.

I use the open source ones from talkytoaster: http://talkytoaster.co.uk/ukmaps.htm

For OS maps you can only use the ones purchased from Garmin not from anywhere else. Read up on the T&Cs as well before buying from them as they are quite strict on licence transfers if you were to replace gps unit in future. I think you would need to buy new maps. Same if you lost your gps and bought new one, think the maps are “locked” to one device.

I can also recommend the open source ones as above. Not as good as OS maps but great for being free.

Thanks for the advice; free maps do sound good!