It's 100% in Hammerfell. If someone tells you the trailer is in

Hammerfell, Elder Scrolls

Starfield' Trailer Reportedly Offers Clue About 'The Elder Scrolls 6' Map

Is it possible to make an Elder Scrolls game with all of Tamriel as a map? - Quora

Out of bounds Skyrim region (approximately Taneth, Hammerfell) vs. TES:VI Trailer [Reupload because of false copyright claim - see pics/captions] : r/ElderScrolls

Morrowind Nexus - mods and community

Cant wait for TES VI Hammerfell! : r/ElderScrolls

The Elder Scrolls Online – Leaked Info So Far

If you were reincarnated into the Elder Scrolls Universe, what race would you be and where would you be from - ignore the inaccuracies on the map, ie - Tear and Mournhold

What does Todd Howard mean by wanting Elder Scrolls VI to be the 'ultimate fantasy-world simulator'? - Quora

Something about Hammerfell is so unique and different, borrowing heavily from Arabic Fantasy and North African Influences, what tropes and influences would you like to see in a game based in Hammerfell?

Elder Scrolls V: Skyrim - Opening Dialogue