Its a GPX file. Pure human-readable TEXT.
Just hand edit the parts you want (either from the AllTrails file or by combining individual trail files), fix up a few of the tags, and you have a new custom gpx file with your desired trails.
KISS
Doug
For those who might be unfamiliar with the acronym: KISS=Keep It Simple Stupid
Which is easier - editing a text file (XML - must keep the formatting correct) or looking at a map of a region and shift-selecting the 5-10 trails I'm likely to want?
In this case, the latter is much simpler. Editing the text file means I need to identify all the trails by name, search them out, and copy and paste them. Certainly I can do that, and may well break AllTrails into more useful clumps.
Being in the user interface world myself, I am floored that selecting 5 tracks and then 'upload to device' actually tries to upload all 396. Who here believes that selecting 5 of 396 files in "My Documents" and pressing delete should delete all 396?
Imagine I am planning the Presi Traverse and I want to have all the likely trails and escape routes (from http://www.chauvinguides.com/presitraverse/presiescapeguide.htm) as tracks. How much faster would it be to add to the selection as you went across the range / down the escape route list and simply hit a button at the end?
Sorry, Doug, I am a big believer in KISS, but there is no way editing the .gpx files by hand is simpler.
Tim
p.s. apologies for the hijack.