编辑“人口”（章节）

=== Pop growth ===
[[File:Update 3 growth surface plot.png|right|thumb|300px|Growth as a function of planet capacity and population]]
{{icon|growth speed}} '''Pop growth''' represents the increase in population from natural reproduction and immigration. A new pop appears after <math>100 + (\text{growth required scaling} \cdot {\text{total empire population}})</math> growth points have been accumulated; the [[Game settings#Game Details|growth required scaling]] is a game setting. The base growth rate is determined by the number of pops on the planet along a [[wikipedia:logistic curve|logistic curve]] determined by the {{icon|planet capacity}} [[Celestial body#Planet capacity|planet capacity]], then pop growth modifiers are applied, and lastly pop growth from immigration/emigration is added/subtracted. The [[Game settings#Game Details|logistic growth ceiling]] game setting determines the maximum base growth.

Any species existing on the planet or which has immigration access to the planet may be selected to grow there. When choosing a species to grow, planets will generally prioritize species that are under-represented on the planet and have citizenship equal to that of the already existing species. If immigration access is lost to all planets containing the currently selected species, a new species will be selected and all existing growth progress will be erased. Species can be chosen manually for growth if the Population Controls policy is set to ''Allowed''. 

{{iconify|Habitability}} is an important pop growth modifier. Pops with very low habitability for a planet will only slowly reproduce or migrate to it or may not at all.

Pop growth stops when a planet is 15% overcrowded and has 5 pops without housing. Pops start to decline when a planet is 25% overcrowded.

{{icon|planet capacity}} [[Celestial body#Planet capacity|Planet capacity]] is capped at 500, regardless of free housing or unblocked districts. However, pops over 500 will not stop growing or decline until required housing exceeds available housing by 15% or 25%, as normal.

{| class="mildtable" 
|+ Base population growth formulas
|-
! Condition
! Formula
|-
| style="border-right:solid thin #ddd; padding-right:0.5em" | <math>\frac{{\text{planet capacity}}}{2} > {\text{planet population}}</math>
| <math>\text{total base growth} = 3 \cdot \max (0.125 \cdot (\text{population} - \frac{\text{population}^2}{\text{planet capacity}} - 1) , 1)</math>
|-
| style="border-right:solid thin #ddd; padding-right:0.5em" | <math>\frac{{\text{planet capacity}}}{2} \le {\text{planet population}}</math>
| <math>\text{total base growth} = 3 \cdot 0.125 \cdot (\text{population} - \frac{\text{population}^2}{\text{planet capacity}} - 1)</math>
|}

Total base pop growth is between 0.3 and <math>(\text{logistic growth ceiling} \cdot 3)</math> (default 4.5) growth per month. Pop growth modifiers, including habitability penalties, are then applied, and then population growth from immigration/emigration is added/subtracted.

==== Migration ====
[[File:Species_right_migration_controls.png|Migration|x24px]] '''Migration''' is calculated by subtracting '''emigration push''' from '''immigration pull''', both of which are determined by factors such as {{iconify|housing}}, {{iconify|stability}} and {{icon|unemployed}} unemployment. A planet with more emigration than immigration will have its {{iconify|growth speed}} lowered and the amount lowered will be added to potential immigration targets. Planets with higher immigration pull will receive a greater share of this migration, which is converted directly into pop growth. Signing a {{iconify|migration treaty}} will allow migration to and from another empire's planets. A newly colonized planet gains {{green|+100}} immigration pull and divides a total of {{yellow|+50}} emigration push between all developed planets, until {{icon|time}} 15 years have passed or the colony has 10 {{iconify|pops}}.

==== Growth weight ====
The exact mechanics by which a new pop is selected for growing/assembly is not fully known. However a bunch of values can be extracted from the {{path|common/defines/00_defines.txt}} file.
{| class="mildtable"
|-
! Name !! Value !! Description
|-
| New_Pop_Species_Randomness || 0.5 || The higher this is, the more random species selection of new pops will be
|-
| New_Pop_Same_Species_Weight || 1.0 || The higher this is, the more new pops will be weighted by number of same or subspecies pops
|-
| New_Pop_Exact_Species_Weight || 0.5 || The higher this is, the more new pops will be weighted by number of exact same species pops
|-
| New_Pop_Slavery_Weight || 0.25 || The higher this is, the more new pops will tend to be balanced between enslaved and non-enslaved species
|-
| New_Pop_Species_Div || 0.05 || The higher this is, the more planets will tend to grow species that are underrepresented on the planet
|-
| New_Pop_Habitability_Threshold || 0.75 || If habitability is under this, apply exponentially increasing penalties to new pop weight
|-
| New_Pop_Homeworld_Mult || 2 || Pops have increased weight for growing on their homeworld
|-
| New_Pop_Growth_Mod_Mult || 0.33 || How much does species growth mod trait matter for new pop weight
|-
| NEW_POP_Immigration_Mod_Mult || 1 || How much does species immigration growth mod trait matter for new pop weight (when there is immigration)
|-
| Pop_Decline_Threshold || 3.0 || A species will decline when there is another species with a growth priority this many times higher
|}