There are numerous tourist maps of the island of Santorini. I have not yet discovered a really perfect topographic map. There are a few maps from Greek providers that are slowly becoming usable, but if you are hiking, you should compare these maps and the satellite images from Google Earth View and possibly also print out photos from Google Earth View. In this Google program you can also build kmz files yourself in which you can save your routes. I originally installed a Google map here, but now that Google wants to make money with it, I had to deactivate it again. Incidentally, Google Earth View also works on smartphones and internet reception is available almost everywhere on Santorini with the corresponding data tariffs. Combined with GPS, you can always determine exactly where you are. Very helpful when hiking! You can also use the GPS2Google app to record your routes and later track them in Google Earth View.
Anyone interested in geology can also order the geological map of Santorini from Spyros Staridas, which is also suitable for non-professionals.