Well, I tried to get something started. I've made the land using Photoshop's Clouds filter/Threshold approach. Then I painted the land and water grabbing the colors from Open Street Map.

I put into Inkscape and was able to make a path from the coastline and from that I did the dashed line to represent the political limit of the city.

Arcádia.png

Then I found a neat tutorial in Wikipedia (here, found is this page along others) and had an idea about how to make different ways (roads, streets, bridges, etc) have a nice contour and still be connected. As I did in this little test:

path21716.png

What I did was basically set the stroke style to a large width (10px) then duplicate the path, reduce the width (to 8px) and change the color (this is described in the aforementioned tutorial). To make it all connected, I used two layers (streets and bridges) as sublayers of another. Then I duplicated the whole base layer and put on the top of the other. This way the shrunk duplicates cover the lines of the other when they intersect.

The major problem will be if they DON'T intersect. I'll have to organize it into different layers to make it work. I also don't know if it will looks nice in different levels of zoom (that's why I still consider the GIS approach).

I'm still looking for help, if there's any better approach to it.