Well, what I did in my Oten-Jo map to keep it looking hand drawn was to draw everything out with a spatter brush at various sizes (15 to 50) and set to fade over a variety of distances (25 for some of the windows to 9000 for the riverbank at one point). Each object was done by hand separately (you could easily duplicate or cut/paste instead once you have a few good examples), what I did was I had the basic picture on a layer, then above that would outline/trace with the brush, simulating brush strokes. Once I had the outline of the house done, i would hide that layer (or sometimes keep it visible to start getting variations) and trace a new house on the layer above that. At some point I would go back through one at a time with a smaller narrow brush to draw windows and doors. Then with a wider brush, under each tracing add a new layer with the lighter shading, follwed by another layer with the darker shading (less wide but above the light shading layer), and finally draw out a chunk of solid white on yet another layer underneath the shadings - then merge the layers for each house. Yes, each object was 4 separate layers at some point. They needed the white background for each individual house to prevent other lines from showing through once I arranged and stacked them. After I had enough houses (I think 120 or so) i started arranging the layers. a similar process was used for the mountians/hills in mine, that would be used to good effect in yours, plus on the forests if you draw the trees individually. I wimped out at that point and did the forests as large irregular elliptical clumps, but I used the same technique to shade them on each layer underneath.
Whew. Sounds a lot more complicate than it really is, it's not nearly so bad once you've done a few. But it is a lot of work and still quite tedious, though a lot of the tedium could be removed by the copy/paste or duplicate method, then maybe run some filters at low settings to give them individual variations.