Introverts like mountains while extroverts like the flatlands, according to this research that graphs out flatness and extroversion by state and shows a relationship. Also they say extroverts like beaches while introverts like mountains.
I'm half-n-half -- neither introvert nor extrovert. (Apparently there's a word for this: "ambivert".) I land in the middle on the "introvert-extrovert" scale on Big 5 and Myers-Briggs personality tests, and it seem to fit as I can be by myself for hours and I don't mind and I can be with other people for hours and that's fine, too.
Having said that, the flatlands vs mountains theory is new to me and makes no sense. It seems like, some people, like my mom, like the "big sky" feeling that you get in a place that's very flat. Others like the scenic feeling from mountains. When you get very high up the scenery becomes quite dramatic.
My mom grew up in west Texas and I've been there many times to visit my grandparents and it is the flattest place I've ever been. The graph shows North Dakota as the flattest state, and I guess the problem here is they're using whole states and some like Texas are pretty big. Texas has some hills on it's eastern side where it borders Louisiana. But on the western side, well, I've been to both North Dakota and west Texas and I can tell you west Texas is flatter.
I live in Denver and maybe Denver is the perfect place for the half-n-half ambiverts who are neither introvert nor extrovert, but something in the middle. Look east, and you're on the flatlands. Look west and you're in the mountains.