The upper thing is a map of the nine worlds of Yggdrasil. Most people draw them as separate world/planets/dimensions, but there are a few inconsistencies with that. To get them out of the way: Thor's said to go East when hunting trolls, the Aesir had a wall built around their fortress to discourage jotunns on the borders, Helheim is sometimes conflated with Niflheim, and the sea appears to be ever-present So they're all connected. Except Midgard because it's special. Some of the more important areas are marked, and a rough approximation of what it looks like from the outside is shown lower. That being said, I might revise this in a bigger, more detailed map later. Below that is a diagram detailing the differences between trolls, jotunns, and thurses. The truth is the difference is very hard to discern. Some beings are very clearly giants, some are trolls, and some waver between the lines. Even in their origins they're similar. Ymir's sweat became a legion of jotnar, his armpits produced a pair of jotunn, and his legs produced a monstrous, six-headed giant; trolls too descend from jotun, specifically Loki, and the words thurse and troll are etymologically similar. So here's my approximation of it: jotunn are basically wild gods, aging slower and having great, fantastic powers, trolls are to jotnar what humans are to the Aesir, and thurse are any monstrous giants, usually characterized by lesser intelligence, solitary attitudes, polycephaly, enormous size from which they can't shapeshift out of, or cannibalism. As with everything I do, it may change later.