From first principles, off the top of my head I’d suggest something simple like the following:
- unambiguous continuous path which is easy to follow
- a continuous path which may become faint or indistinct, or has minor gaps with the next section clearly visible (stream crossings that aren’t well marked, a very short area with more vegetation, etc). It doesn’t require routefinding to follow but someone might have to stop and look for it occasionally
- a path which mostly exists, but requires routefinding to find the next section at times
- a path which mostly doesn’t exist, and requires routefinding the majority of the time
- no path exists in any meaningful way
Simple and non-overlapping, aside from defining the ‘small gaps’ in good in a clear way.
Trying to break this into 6 (actually 7 if no doesn’t mean no but ultra_horrible) definitions causes a lot of arbitrary break points.