A mistake that creeps in to a lot of work is the monoculture – the whole idea that all x share the same views and culture. That tends to tag onto the notion that culture is both somehow genetic and consists of interesting costumes and food.
I can’t really blame schools for this, not entirely, since they don’t have the time to go into the details enough to cover much more than interesting costumes and food, and not many people are capable of twisting their mind through the kind of maneuvers that let a person have a decent grasp of how a different culture works.
Suffice to say there is not ever a “national” culture unless the nation is very, very small and very, very homogenous. And possibly not even then. Even tribes can host multiple cultures within their population (trust me on this: the moiety systems used by some of the Australian tribes amount to parallel cultures within each tribe, and when said tribe has eight moieties each with its own distinct set of traditions that tribe hosts at least that many cultures – Dave probably has a whole lot more to say on that topic, and more knowledge, at least of the African cultures around where he used to live).
Rather, there are national traits that can be considered broad generalizations. Americans tend to be straightforward and somewhat prudish by Australian standards. Australians tend to be fond of word-play (it’s something of a given when your dialect is a mutated thieves cant) and generally regard authority as something to be ignored whenever it can be done without getting caught. Both are pretty much classless societies in that a random American or Australian is probably going to view a random person on their merits and not look for markers on their social status. I don’t know enough of them to say for sure, but I gather most European cultures will look for class markers and judge by them.
Within those big, overarching groups, you get smaller cultures. Each city has its own feel. So does each town. How distinctive that is depends on how much the local traditions have been able to grow without having new people coming in to disrupt things – and no matter what their intentions are, new people in sufficient quantity will always disrupt things. They can’t help it. A baby boom will do the same thing just by being more bodies than the local infrastructure can handle.
Where it’s difficult to travel from one place to another, local traditions will develop and come to form a local culture. There will be things people in that area do that are passed on through generations until it seems almost instinctive. Enough generations pass without much contact, and you wind up with villages where the local dialect is damn near incomprehensible to someone from the next valley over.
I can totally see the same dynamic happening with space stations or isolated colonies: the distances involved even if the lightspeed barrier is overcome mean that it’s unlikely to every be easy to travel between them – heck, it’s not technologically easy to travel long distance now and that’s with air travel having become sufficiently common that there aren’t that many barriers to it (or weren’t until recently). Add an ocean crossing or two to the mix, or look at travel between say a Moon base and Earth, and it’s going to be a major and expensive undertaking for a long time.
Which means we’re going to have interesting cultural development happening as soon as we start having people figuring out how to live permanently in a location that isn’t this planet. Some of it will be differentiation, with people picking up habits related to what they do as they adapt to the local environment. Some will be unification with people who are in the colony or community building traditions together by virtue of living in more or less the same location isolated from anyone else.
Fast-forward enough generations to have the original settlers no longer able to tell people the real reason things were done (you all remember the tale of grandma’s baking dish and the leg roast, right?), and you got a set of intertwined cultures. It’s how they grow.
Oh, and don’t ask me how I got to this point after thinking about Australian traditions on ANZAC Day and how they’ve become an integral part of the broader Australian culture over the last hundred or so years. Because I don’t know the answer myself.