From what I currently understand, the map is created by Google My Maps. You are able to create a map and set markers and new layers. Each marker can have a description and name. Layers can also be set and possibly be a way to sort what type of establishments there are. I don't know about it publicly being open to edit, but it is possible that you could create a forum and allow players to list their establishments to go onto the map. Also, fantasy locations could be an issue. For fantasy locations that are in a real country, state or province, the player would have to list where it could possibly be as a real location. For fantasy locations that have its complete own world, from what I can currently see, it couldn't be listed properly.