I used https://www.openstreetmap.org/ to download specific maps and then edited out all but the roads in Illustrator. My goal was to score the lines of the map instead of engrave so I needed everything to be a vector. I did some test runs on some MDF which I was pretty happy with. What you see in the pictures was done on ProofGrade Medium Maple Plywood (default settings) which made the line work really stand out on the light wood.
I made these 4x4" coasters for my mom with the road maps pertaining to the locations of family. Really dense city centers with the close together lines typically burned or crumbled out of top layer of plywood. All line work was “scored” and the text and river were engraved. Typical time was 12-20 minutes.