This is one of the many occasions that calls for something called wide format printing, a method of printing patterns and letters onto large pieces of vinyl.
Maps are especially difficult to produce otherwise, and this is the strong point for wide format printing, getting lots and lots of details into one small area without any loss of quality.
This particular case also has a thick protective layer of clear vinyl placed on top of the printed vinyl.
This style of sign belongs to the wide format printing category. Click on that link to see more kinds of articles like this one.