I like it, it conveys a very neat idea of just how distant everything is. The way you've done the towns and cities it doesn't even need a scale on the map, you can get a very good idea just by seeing the buildings and their relationship.

As for the forests, one thing I'd try is this.

Get the forests on their own layer. (very important)
Select the area outside of the forests.
Go 'Select' -> 'Modify' -> 'Expand' and expand the selection by maybe 10 pixels. (How much to expand it depends on what resolution you work with).
Go 'Select' -> 'Modify' -> 'Feather' and feather about 5 pixels.
Hit the delete key.

And you'll have the edge of the forest neatly fade away instead of abruptly ending. This should be quite compatible with the blending effects you're already using and might make them work even better (as always with photoshop, play around a bit, try different combinations and see what works for you).