The Witcher 3: Wild Hunt’s world map isn’t just one big area, it’s split into six, one small prologue map named White Orchard where you will begin your journey in, and the rest of them are: Vizima, Velen, Novigrad, Skellige Isles, Kaer Morhen. Going from one region to another is where you’ll encounter a loading screen.
On the west side of the world map you’ll see a bunch of islands, and that area is named The Skellige Isles which is only access via a loading screen boat ride sequence. There’s also a few areas which can only be accessible via fast travel through the game’s map like the Royal Palace in Vizima.
There’s also a different type of map / world that the developers are calling ‘non-natural’ and they’re keeping it hidden at the moment.