This article is for the PC version of Stellaris only.
Population, also known as Population units or Pop, is the center of productivity and political action within the empire. They provide resources by working on districts and buildings, and influence if they are part of a specific faction.
Each planet has four variables that determine its demographical direction:
Pop Growth represents the increase in population from natural reproduction and immigration. 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. Habitability is a major factor in Pop growth. Pops with very low habitability for a planet will only slowly reproduce or migrate to it or may not at all. Species can be chosen manually for Growth if the Population Controls Policy is set to Allowed.
Pop Decline represents the decrease of certain Species on the planet from emigration and purging. Overcrowded planets that have over-represented species will have those species begin to decline in numbers and be replaced by newly growing, under-represented species that have equal citizenship. Purging a particular species will essentially guarantee that species' rapid decline as well as creating massive amounts of emigration in the form of refugees if displacement is used.
Pop Assembly represents a planet's capacity for constructing Mechanical or Machine Pops. Roboticist Jobs add +2 Monthly Pop Assembly Points and Replicator Jobs add +1 Monthly Pop Assembly Points. Once 100 points are reached a new robot pop is created on the planet. Non-sentient robotic pops do not migrate but can create overcrowding and unemployment. Templates can always be chosen manually for Assembly.
A planet can have only one growing Pop, one declining Pop and one assembling Pop at any time.
Migration is calculated by subtracting Emigration Push from Immigration Pull, both of which are determined by factors such as housing, stability and unemployment. A planet with more emigration than immigration will have pop decline where the removed pops are distributed among potential immigration targets. Planets with higher immigration pull will receive a greater share of this migration, which is converted directly into pop growth. Signing migration treaties will allow migration to and from other empires and accepting refugees will also create immigration from planets outside the empire borders. When a new planet is colonized existing worlds will get +50 Emigration Push while the new colony will get it will get +100 Immigration Pull.
The exact mechanics by which a new Pop is selected for growing/assembly is not fully known. However a bunch of values could be extracted from the defines file.
OVERCROWDING_NO_GROWTH_THRESHOLD = 1.5 # At this amount of overcrowding, growth stops entirely OVERCROWDING_DECLINE_THRESHOLD = 2.0 # At this amount of overcrowding, pops start declining NEW_POP_SPECIES_RANDOMNESS = 1.0 # 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 = 0.5 # The higher this is, the more new pops will tend to be balanced between enslaved and non-enslaved species NEW_POP_SPECIES_DIV = 0.5 # The higher this is, the more planets will tend to grow species that are underrepresented on the planet NEW_POP_HABITABILITY_THRESHOLD = 0.6 # 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_ASSEMBLY_TRAIT_MULT = 1 # Extra weight per trait point for assembled pops NEW_POP_GROWTH_MOD_MULT = 0.66 # 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_ENSLAVE_MAX_RANK = 1 # Pops above this stratum rank will not be enslaved from civics, etc
BASE_POP_DECLINE = 5 # Base decline rate of pops REQUIRED_POP_DECLINE = 100 # Required decline to remove a pop POP_DECLINE_THRESHOLD = 3.0 # A species will decline when there is another species with a growth priority this many times higher
MAX_EMIGRATION_PUSH = 100 MAX_GROWTH_FROM_IMMIGRATION = 5 MAX_GROWTH_PENALTY_FROM_EMIGRATION = 0.95 # Fraction of base monthly growth
Each pop in an empire has a base happiness rating. It ranges from 0% to 100% and has a base level of 50%, and together with the Stratum's political power determines the Approval Rating, in addition to the following effects:
- Each point of Happiness above 50 adds +1% Governing Ethics Attraction to free pops and +2% Authoritarian Ethics Attraction to slaves.
- Each point of Happiness below 50 adds −1% Governing Ethics Attraction to free pops and +10% Egalitarian Ethics Attraction to slaves.
- Each point of Happiness above 50 gives each pop −0.02 Crime, up to 0 per pop at 100% Happiness
- Each point of Happiness below 50 gives each pop +0.02 Crime, up to +2 per pop at 0% Happiness
Fortunately, there are also many ways to improve happiness in an empire. Planetary edicts, civics, traditions, buildings, planet modifiers and ruler traits can positively affect happiness. Events may have an impact on planetary or empire happiness for a limited time as well.
Approval Rating ranges from 0% to 100% and has a base level of 50%.
- Each point of Approval Rating above 50% adds +0.6 Stability, up to +30 at 100% Approval Rating.
- Each point of Approval Rating below 50% adds −1 Stability, up to −50 at 0% Approval Rating.
Organic pops consume 1 Food per month. Robots instead consume 1 Energy per month. In addition, biological pops that are not part of a Gestalt Consciousness empire require a certain amount of consumer goods based on their living standards. Synthetics that are given Citizen rights require it as well.
Housing represent the living space available for pops to live comfortably. Housing is primarily provided by districts, with City districts giving more housing than their resource-focused alternatives. Each pop requires 1 unit of housing by default but the housing demands of individual pops can change due to a variety of factors. If the number of pops exceeds the amount of housing it will cause −1% happiness and +30 planet emigration push for every negative unit of Housing.
As a rule of thumb, each resource district exactly pays for itself in terms of housing, while the pops that work building jobs need city districts (or housing buildings) for their housing, though the capital building provides some buffer before cities are needed. This applies equally to ecumenopolises, but not to habitats, where non-residential districts provide no housing at all. The Agrarian Idyll civic gives extra housing to resource districts, allowing the empire to house its pops working building jobs mostly via resource districts.
Amenities represent the infrastructure and jobs dedicated to fulfilling the needs of the population. Individualist empires obtain amenities from a variety of jobs while Gestalt Consciousness empires obtain them primarily from Maintenance Drone jobs. High amenities cause increased happiness to biological pops and increased stability in Gestalt Consciousness empires, while insufficient amenities will lower them.
Political power and stratum
If a pop takes a job above its stratum it will be promoted to the higher stratum. If there are no available jobs of equal or higher Stratum the pop will become unemployed, slowly demoting in stratum and causing happiness penalties at most levels of living standards.
Authoritarian empires have access to the Slaver Guilds or Indentured Assets civics, which will enslave up to 40% of pops on every planet regardless of citizenship if there are not enough alien pops with Slavery citizenship to fill the quota.
Robots are automatically enslaved if the Synthetics technology is researched and Artificial Intelligence Policy is set to Servitude. In Synthetic Dawn this may cause an AI rebellion.
Enslaved pops also use only 0.75 amenities and 0.75 housing instead of 1, and can be further reduced if the Slavery type is Servitude or Livestock. They also get -50% Resettlement Cost. Enslaved pops cannot join Factions and have only 25% Political Power, or 0% if a Slave Processing Facility is present on the planet. However they can still increase Crime if they're too unhappy.
Slave Output can be affected by the following:
|Slaver Guilds civic||+10%|
|Indentured Assets civic||+10%|
|Iron Fist governor trait||+10%|
|Slave Optimization agenda||+10%|
|Workplace Motivators tradition||+5%|
|Slave Processing Facility building||+5%|
|Slave Riots planet modifier||-100%|
Ethics attraction modifiers
Ethics divergence is where a pop or group of pops decide to follow a different ethic than the general population. A materialist pop may decide to follow a more spiritual path and a pacifist culture might decide that peace is the path of the weak.
Each pop in an empire will only embrace a single, non-fanatic ethic. At the start of the game, the population will be made of the ones that were picked. As population expands and eventually is divided over various planets and sectors, certain segments may decide to adopt values that are different from the core values of the species due to various circumstances in and around the empire.
Each ethic has a certain attraction value attached for all pops, depending on both the empire's situation and their own. For example,
- enslaved pops tend to become more egalitarian;
- fighting a lot of wars will increase the attraction for militarism across the entire empire.
The exact values and options that influence the attraction levels of certain ethics can be found at ethics attraction.
The attraction factors of ethics can be amplified by certain actions such as enacting policies or having traits. Governing ethics attraction can be modified by policy, edict, or through promoting or suppressing political fraction.
Having a positive ethics attraction effect will let all actions that increase attraction to the government ethics result in even more attraction, and negative amounts will be decreased. With a modifier of 50%, an action that would increase attraction by 2 would instead increase by 3.
Robots are artificial pops and can be constructed once the required technology becomes available. They have the Mechanical trait, giving them +200% habitability on any planet. Robots can be given new traits via robo-modding and the template with the highest number of used trait points will be built by default. A different template can be specified for each planet.
The jobs a robot can have are limited by the highest robot technology researched. If an empire researches the Synthetics technology, robots can be given sentience, which lets them be affected by happiness and have ethics.
|Tech level||Maximum stratum||Can colonize||Sentient|
|Robotic Workers||Worker (except Technician and Clerk)|
|Synthetics|| if AI policy is set to Outlawed
if AI policy is set to Servitude or Citizen Rights
Robots without Citizen Rights require 50% less housing and amenities and do not need consumer goods. If a planet with sentient robots is captured by an empire that doesn't have the Synthetics technology, they lose their sentience, and if a planet with non-sentient robots is captured by an empire that has the Synthetics technology and does not have the Outlawed Artificial Intelligence policy, they are immediately given sentience. Spiritualist empires cannot give them citizen rights.
|Available only with the Synthetic Dawn DLC enabled.|
As long as synthetics are present within an empire with the Artificial Intelligence policy set to Servitude, there is a risk of them starting the AI rebellion event chain. See AI rebellion for details.
Purges represent the systematic elimination of specific pops or entire species from an empire and can be done on a per pop or species basis.
Targeted pop purging still requires applying the species-wide slavery at minimum and it is limited to a basic extermination, although without production penalty. Gestalt Consciousness can purge their pops of any composition freely, with exception of Bio-Trophies.
Species-wide purging is done by setting the species' citizenship to Undesirables. Gestalt Consciousness pops in empires of different authority are automatically set as Undesirables too. Therefore gaining planets from a Hive Mind empire means that the planet will be lost when it is empty of pop if there is not at least 1 Pop of the conquering empire's species on it. There are also three special cases:
- Pre-Sapients can only be purged if the Pre-Sapients policy is not set to Protected and are automatically purged if set to Extermination.
- Robots are automatically purged if the Robotic Workers policy is set to Outlawed.
- Synthetics can only be purged if the Artificial Intelligence policy is not set to Citizen Rights.
Having any pops marked as undesirable is a negative issue for Xenophile factions. Depending on the purge type, a timer will be started for all pops (see Purge time below). When the time runs out, the purge is completed: all remaining pops of that species will be removed from the empire's planets. Unless the purge type is Neutering or the pop was pre-sentient, robotic or a Gestalt Consciousness, an opinion penalty will be applied to all other regular empires based on the number of pops purged, depending on various modifiers. If the empire has the same primary species as the purged pops, the penalty is always −25 per purged pop. These stack up to −1000, making genocide a dangerous approach.
There are multiple types of purges available, determined by the Purge Type species right.
Pops from other empires may flee to escape purges, slavery, resettlement, crisis bombardment or as a result of land appropriation. Whether another empire is willing to accept those fleeing depends on its Refugees policy. An empire can choose to accept other species with open arms, allowing refugee pops to freely move into their empire; be more restrictive and accept only those pops that the empire has deigned to grant citizenship; or simply shut down acceptance of refugees altogether.
Refugees can be used to help grow an empire as well as gain access to new species as persecuting empires are unlikely to favor migration treaties in the first place. However, refugees may introduce ethics which are radically different to an empire's. Accepted refugee pops will get a temporary +20 happiness.