Ok, so I'm fairly new, just got the key a week ago.  Didn't really know what to do, so I set up camp near Boston and levelled up some basic skills, meaning to go further to set up a permanent claim later.  Got a shock this morning when I found my leanto was gone, I'm assuming it was just decay because it wasn't on a claim.  (Does being on a claim slow down decay?)
Anyway, so I walked South a LONG way and got the message about arriving in the wilderness.  Which was what I was aiming for.  I wanted to set up somewhere just outside that.  But after I went North again, there was no indication I'd left the wilderness, and going South didn't indicate that I was back in it again.
You can see personal claims and town claims.  Is there any way to reliably tell where the darkness is?  
I have set up a claim now, I think I'm quite a bit North of that now, lol, I got very frustrated looking for the 'perfect' spot.  But I'd still like to know what the go is with the darkness.  And yes, I know it's darker.  But it seems to get gradually darker.