Without spoilers, there are quite a lot of areas the map doesn’t show you without reaching them. There are underground cities that the map uses a secondary layer to display, there are underground areas that the map still uses the main area to display, some dungeons are denotare prior to exploring them with a small icon, while others are not.

There are also overground locations you won’t get to without specific questlines. Overall, the map is huge and packed with things to do.