Trying to fix part of my previous map just screwed it up as I had all my images in the same photoshop layer. Duh! So I cribbed from this great tutorial to use layers properly and made, to my eye, a much better map.
Anyway, if anyone finds this useful and makes their own maps as a result, do share what you produce! Also, if you have any suggestions for making my map better, do leave a comment.
EDIT - just noticed, this is my 100th post. Yay for me!