When I want to populate a fantasy world with different regions and their cultures, I have problems knowing where to start.
Recently I used a quick-and-dirty technique that I could call "cultural mash-up". I note down that a particular area is a (-n unlikely) mix of e.g. renaissance Italy and medieval Japan (and my poor understanding of them at that), and use that to ad-lib and improvise features of the people and culture. It works OK at the gaming table, in that I can often generate an answer to a question.
However, it is hard for me to generate more structured source material based on that. The problem is not a lack of ideas, but a lack of structure to decide what should be relevant, when I want to present a view of the culture as a whole to someone else. I don't really want to present the mashup idea directly ("this place is like a mix of Italy and Japan"), as it is an idea generator, not the right level of descriptive information to get someone immersed in a game or story.
I would like to be able to generate 3 or 4 pages of source material (from 1000 - 2000 words) as a short introduction to each fantasy culture. Assuming I have less than 10 "major" cultures to document, this seems like a good compromise between amount of work to produce (maybe 40 pages), and benefit (someone could read a brief introduction to one culture in under 10 mins).
What sort of information should be in that introduction? I suspect a lot will depend on genre, and the world setting - so, if it helps narrow the question, this is for a fantasy RPG world, and I am a fan of Glorantha and other non-Tolkein-but-still-fantasy worlds. I expect I will also need to set general norms for the world, against which different cultures might be considered more or less friendly, open, religious, organised etc etc.
To avoid the answer being a list of subject titles, I am looking first and foremost for an organising principle. Without having qualifications in History or Sociology, how do I tackle describing the nature or "personality" of a culture?