on CotI by Supplement Four
which is of great inspiration for my setting. Though things would be less extreme in my version, non-habitable worlds would draw very little populations. Especially waterless and/or corrosive/insidious hellholes - Tertiary systems. Secondary systems have surface water, either liquid or easily accessible ice. Primary systems have atmosphere 4-9 and hydrographics 4+.
Usually a Tertiary system, barring major mineral wealth, would only have a tiny outpost if it's in the way to more interesting worlds, or even be uninhabited (and not too thoroughly explored) if it does not stand on a trade route. Of course, strategically important Tertiary systems might have a more significant presence, usually a military base or fort of some sort. Secondary systems usually have a colony of some sort, but it is rarely large as most people won't be interested in living in such a place - this rarely goes above a few million inhabitants even if there is vast mineral wealth around. Most people live on Primary worlds.
_________________We are but a tiny candle flickering against the darkness of our times.
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