Thanks very much for your reply. I was thinking that it was as simple as matching them to the road lines and then moving "out in a certain direction" but that shows my naïveté, I think! If you do come up with something, that would be awesome.
Oh, and one more thing came to mind as I was having a play the other day. What would it take to add a "forest option"? In other words a green expanse outside the city environs proper (perhaps with the option of 'partial' ( self contained forest on the map) or "full" a forest that encompasses the background space around a settlement? It could simply be another color, no need for tree symbols or anything but have a "foresty" edge to it ... again, am I asking a bit much? Ideally, if it could be "populated" with your tree symbols - a bunch of them - I think it would look fantastic.
Love your work. Thanks again.