Sociological or anthropological studies on insular or peninsular cities?

Try looking at the Journal of Island Studies.

Urban sociology, at least, doesn't necessarily hold that kind of material determinism to be true. So when you say cities that are built on islands or peninsulas, or in geographically isolated areas, develop and behave differently from cities that are more easily and fully connected to other cities you're making a pretty big empirical claim right there which may or may not be supported by evidence. So if you don't find work that discusses these issues, it might be because this assumption is unproven. You might want to look at architectural history than sociological or anthropological work, in general.

I agree that the claim that islands/peninsulas develop and behave differently than more connected cities may indeed beg the question, but do also believe that there is something to the idea that how the people who live both within and on the outside of these (physically or mentally) isolated communities see themselves (i.e. how this affects their expression of community identity) in comparison to one another can lend a lot to how they develop - and may in some cases lead to them developing along different wavelengths. One sees this frequently in minority groups where the expression of identity becomes stronger in comparison to the majority culture. I think there's a lot to be explored in this topic and that other avenues to look into would be expression of ethnicity/identity. I do also think that this type of expression probably has become less common in the modern world, given how connected we all are now (physically due to modern transportation, but also because of the internet), but there are still pockets of it due to political isolationism (e.g. North Korea or Cuba). This is making me wish I had more of my grad school materials here. I also took a seminar on ethnicity, but don't have access to the reading list for it. Unfortunately, that's all the way across the country at my parents' house.

if you don't find work that discusses these issues, it might be because this assumption is unproven. I'm not looking for your opinion or your speculation. I'm looking for actual writings on the topic, which I believe I have read before.