I could (possibly) work this out myself, but I'll try you lot instead: anyone know how to combine two GPS tracks onto one map? I mean tracks as stored on Garmin's website, and displayed like http://connect.garmin.com/activity/127111491. Specifically, I'd like to combine that track with this one. The tracks are both public, so you don't have to assume any authentication is needed.
Update: thanks for the advice. In the end I didn't bother with any of the fancy software and just used vim which did a perfectly good job of sticking two GPS files together.
It would be nice to colour the tracks separately but I'll live without. I'd still like to be able to do this on-the-fly, but again life is too short.
The answer is: Tidy steered a better course than me :-(.
I've never used garmin's web site but my first thought would be
download the two tracks from the website to local files or upload them directly from your Garmin to files, combine them with gpsbabel, and upload to the garmin website?
I haven't done "mash ups" exactly, but I think if you can export the path into. a KM! Format file you can then import into Google maps with their API.
If you have Garmin's MapSource desktop software there's a handy "join tracks" command. I'm fairly certain that their free Basecamp software has a similar feature. Granted this would require some transferring back and forth between your desktop and Garmin's site but I don't know of a simpler way off the top of my head.
If you have Mapsource (a Garmin product), I think you can merge using copy and paste. Or maybe Track-N-Share (free) will do it?
On the mac I use Adze for that sort of thing.