Very well Sir, as you wish. I shall not argue with someone who won’t even bother to look up what Yggdrasil is or read a single article about the Norse world. I know that there are no nine worlds in the game, but Fjordur is inspired by Norse Mythology and the worlds that are in game (Jotunheim, Asgard, Vanaheim) are directly from Norse mythology. The tree Yggdrasil connects all the remaining worlds which were not added because of performance problems of having such a big map.

If you do actually decide to look into the matter (which I doubt), go read Neil Gaiman’s Norse mythology, specifically the first two or three chapters. It details the Norse world and how it was created, and all the nine realms on the tree Yggdrasil

Have a good day