There are 9 Imperial provinces (I was brought in with Oblivion, that's what I'll base this off of) and we've only seen 2 in full. Morrowind only had you on the island of Vvardenfell. There's Black Marsh (Argonia), High Rock, Hammerfell, Elsweyr, Valenwood, The Summerset Isles, Skyrim, Cyrodiil...