An incident where I shipped population to a planet only to watch the available worker population drop to zero inspired me to look a little harder at how colonies divide up population into Agriculture and Environmental, Service industries and Manufacturing sectors.
So, based on a bit of wiki and forum hunting as well as some reverse engineering based on around 20 colonies, here are the basic formulas:
- Agriculture and Environmental (%) = 5 + Colony Cost x 5
- Service industries (%) = 17. 75 x Population0. 2505 with a maximum of the lesser of 70% and 100 - Agriculture and Environmental (%)
- Manufacturing (%) = 100 - Agriculture and Environmental (%) - Service industries (%)
I checked the rest of my colonies, and these formulas seem to hold.
This led me to a few interesting observations:
- Colonies with a Colony Cost >= 5 have a finite capacity for manufacturing workers that is reached long before the colony hits its Population Capacity
- Colonies hit a local maximum worker population at the total population of (4. 28 - 0. 225 x Colony Cost)4
after that, the worker population will drop until either it hits 0 (for Colony Cost >= 5) or it begins to increase again at around 241. 5m total population when Service industries (%) hits its max at 70% (for Colony Costs between ~1. 5 and 5).
In practice, this means that if you have a colony with a Colony Cost of 2, you shouldn't bother pushing the population beyond 189m unless you are willing to wait for it to get beyond 250m when you will see a net worker increase. The worse case is colonies with Colony Cost close to 5, with a colony cost of 4. 9, you hit your initial max worker amount of 14. 25m at a total population of 100. 8m, but exceed that and you won't see 14. 25m workers at that colony again until you hit 2845m total population.
Up to this point, my policy for marginal worlds that weren't particularly strategic, has been to slap down a colony, feed it some infrastructure and let it grow naturally until it could support some mines and maybe a handful of construction factories to bootstrap it into usefulness, but I often ran into problems that the available worker amount would go negative and no amount of shipping over population would do much to help. These formulas explain why, and I'm not really sure how I want to proceed, probably massive orbital stations that either terraform or strip mine these planets.
This also explains why planets that are optimal to colonize, Colony Cost 0 - 1. 5, still hit a slump between around 200m to 240m total population, around that point virtually every million pop you push in just pushes up the Service industries (%) enough to minimize the increase to maximum available workers.
Here's a quick chart of some of the low to mid Colony Costs for Population vs. Maximum Available Workers. It's interesting to see, and usual to keep in mind when planning colonies and prioritizing terraforming.