If we add all the information about the locations up there will be some loading screens for sure.:crybaby:
Skellige to main land and other locations not directly tied to NML and Novigrad.
Hopefully they disguise them good enough so that we get the impression of 'fully' open world.
To be honest, even if there was a loading screen when passing between all 3 main regions, it would be negligible. Each region equates to an impressively sized game in its own right. I don't necessarily want to, but using Skyrim (because the maths has already been done) as a comparison, Skellige is 1.6 times the size. Novigrad is 2 times. No Man's Land details haven't been divulged to my knowledge, but from what I understand, it's likely to be larger.
Marry this with the apparent philosophy of minimal long-distance travelling, be it to other ends of a territory, or to new lands, it most certainly will be a rare occurrence.
Skyrim was considered a 'fully' open world. And that had loading screens for *every* interior location. That may not be the case for W3, further trivialising three measly loading events.