Frustration in Excelsis 
Worldbuilding Addict
This brief shot gave a lot of information about the state of the hippogriffs and Mount Aris. Just from this brief pan we can see a great many things that were either skipped in the movie or built later in-universe:
Firstly, there seems to be some substantial settlement along the base of the mountain itself, rather than just the city on the summit. Either that just wasn't visible in the movie or -- I'm leaning more towards the second option -- built afterwards. Perhaps the population grew enough during the exile that some extra houses were needed, or perhaps that part was built to accommodate and service the new traffic between the island and the mainland?
On the note of traffic, there's the land bridge. That's definitely new, and I agree with"[@Scintilla Aquila":](/1713610#comment_7077103) -- it's too thin, straight and regular to be natural. That definitely looks like something someone built.
Since Mount Aris was an island in the movie, it'd have to have been built afterwards.
Thirdly, there are the houses and farms around the coast near Mount Aris itself. There's no way to tell if they were built recently or if they're older things reclaimed after the Storm King's defeat, but they definitely weren't present in the movie.
Regardless of the specifics, it's clear that the hippogriff/seapony nation went through a lot of very impressive building and rebuilding since the movie.
Firstly, there seems to be some substantial settlement along the base of the mountain itself, rather than just the city on the summit. Either that just wasn't visible in the movie or -- I'm leaning more towards the second option -- built afterwards. Perhaps the population grew enough during the exile that some extra houses were needed, or perhaps that part was built to accommodate and service the new traffic between the island and the mainland?
On the note of traffic, there's the land bridge. That's definitely new, and I agree with
Thirdly, there are the houses and farms around the coast near Mount Aris itself. There's no way to tell if they were built recently or if they're older things reclaimed after the Storm King's defeat, but they definitely weren't present in the movie.
Regardless of the specifics, it's clear that the hippogriff/seapony nation went through a lot of very impressive building and rebuilding since the movie.