Ive done a bit of raster to vector conversion, and generally the results arent very acceptable, and that was with black and white images, i cant imagine how bad theyd be with colour maps!
On the other hand, i ahve imported a pic of a map in to SU before and traced over the contour lines. That worked pretty well, and if youve got a good pic you can drape it over the mesh very easily. If you had some known distances, i supose you could also do it to scale as well. or maybe just use GE π