[aprssig] UTM, USNG, global applicability

[Jim Lux]

UTM is a worldwide standard (hence the "universal" in universal 
transverse mercator).  I suspect that pretty much everyone uses it in 
some form or another. Sure, the three remaining countries that measure 
things in something other than meters may have a local coordinate system 
based on some other unit (e.g. feet).  But international maps tend to 
have a UTM overprint on the maps.\

There are local variations, e.g. Ordnance Survey in the UK, but even 
then, it's a meter based square grid, and while the "grid squares" may 
not line up with UTM grid squares, the same basic reporting scheme of 
eastings and northings is used. OSNG uses 100x100 km grid squares with 
an origin of 49N, 2W.  For some reason they use the Airy 1830 ellipsoid 
rather than the more modern Clarke 1866 or the WGS 84.. but I'll bet the 
difference isn't significant until you get down into meter scale.