pollution-spread mechanic sourced
Pollution spread
Pollution emitted by sources accumulates and diffuses across land, water, or air cells and harms health, land value, or growth, or provokes threats.
definition
Owns a pollution value per cell or chunk. Each update, emitters add pollution, a fraction diffuses to neighboring cells, and terrain, vegetation, or water absorb some; other systems read the local value as a penalty to health, land value, crop growth, or happiness. Factorio stores pollution per 32x32-tile chunk, updates every 64 ticks, diffuses 2% to each cardinal neighbor once a chunk holds 15 or more, absorbs it by tile type and trees (trees are damaged above 60), and lets enemy spawners absorb it to fund attack waves. SimCity computes a pollution map from industry and traffic that depresses land value; Cities: Skylines separates ground, noise, and water pollution, and sewage released upstream contaminates water intakes downstream. Inputs are emitter locations and rates; outputs are a spatial field read by other systems.
player experience
Growth leaves a visible stain. The player separates factories from homes, plants green buffers, and watches the overlay creep outward; in Factorio a bigger factory directly invites bigger attacks. Cleanup competes with expansion for the same resources.
design levers
- emission rate per source and modifiers such as efficiency upgrades or filters
- diffusion fraction, minimum amount before diffusing, and grid resolution
- absorption by terrain, water, and vegetation, and whether absorbers are damaged
- what pollution affects: health, land value, crops, happiness, enemy aggression
- cleanup tools and their cost
failure modes
- Pollution that only lowers land value is solved once by zoning distance and then ignored.
- Fine-grained diffusion with no threshold or chunking costs compute and produces smeared, unreadable fields.
- Effects carried by hidden channels, such as water contamination far downstream, read as unexplained sickness.
dynamics
- Zoning separates polluting and sensitive uses, which lengthens commutes and adds traffic.
- In Factorio pollution couples production scale to attack size, so efficiency becomes a defense strategy.
- Absorbers degrade under load, so a polluted region can tip into faster spread as forests die.
open questions
- Can learned dispersion surrogates make air and water pollution fields physically plausible while staying cheap and legible?