I echo what jfrazierjr said would go even further. Most often then not, digital artists contracted to create maps or cartography are hired by a large entities or companies ( i.e. tabletop publisher, video game developer, etc). When this happens, the copyright and distribution rights are owned by the company who originally hired the artist in question. So you would need to contact them and deal with their legal departments to purchase the rights and it probably won't be open to the public domain. Most artists and people represented on this forum work for the tabletop RPG market. There's a few people here you can talk to who are excellent cartographers for their IP's but again it probably won't get you anywhere. Mike Schley, Robert Lazzaretti, Jon Roberts, Jared Blando, Matt Goldman are just a few artist off the top of my head who have made some of the most memorable RPG maps. Hope this helps.