I’ve just published a PDF document to my Kofi page, free for current subscribers:

Notes on the Structure of Interstellar Civilizations

This is a collection of assumptions, a bit of mathematical modeling, and lots of commentary on the prevalence of interstellar cultures in the Human Destiny setting. Even if you’re not interested in that setting per se, it may be of some interest as an example of deliberate world-building on a very grand scale.

There’s going to be a follow-on project, involving making some maps of the Human Protectorate’s primary volume, and of the immediate galactic neighborhood around Sol in the Human Destiny universe. Not sure if I’ll turn to that immediately, but it’s in the critical path for my project to re-think that setting, so probably sooner rather than later.