I tried to do this with some old maps I have and wanted a DEM of the map contours and its a hard thing to do. In fact I read a PhD paper on someone claiming to do this and asked some pointed questions to them and their response was "well er.. actually it doesnt work on many maps" yada yada which is about my experience of it. The reason is that unless you use specific maps and specific areas and terrain topology it cant work. The reason is that if you take a normal publication map then usually it prints the contours as a light colour and also its on a layer that is at the bottom of the printing stack. So contour heights, placenames and all sorts of stuff get put on layers which mask the contour. Secondly, on the maps which I had (and I wont mention which....) the contour lines and the buildings are of similar RGB colour so difficult to isolate. But heres the clincher, if you get to a steep ravine or cliff of any sort then all the contour lines bunch up and become a single line.
Ok, so say your map is special and does not have buildings on it and also no cliffs then I wrote a tutorial on how to convert these (usually ones I have drawn the contours myself) into a full pixel DEM. If I cant find the link then ill briefly explain it. Get your contours into black and white. I.e. white background and black lines. No shades of grey just contrast enhance till you lose them. Then using the flood fill tool with black ink, find either the highest or lowest point on the map and fill it. Then miss a contour then fill the next so its like zebra bands of black and white. Then you may want to smooth it to shades of grey and put the contrast back up to max again to make sure you dont leave any 1 pixel holes in it. Then shove it into inkscape and do the raster to vector scan of it in there. By doing the zebra you only get one set of vector lines per contour instead of one per side of the line.
I'll edit in the link if I can find it.
http://www.cartographersguild.com/ho...p-into-3d.html
http://www.cartographersguild.com/ma...d-project.html
http://www.cartographersguild.com/3d...style-map.html
A few posts where I detail that but no actual tut. Still there you go.
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