**Ocean Dead Fraction** — Fraction of biologically dead ocean. Reduces evaporation → inland drought cascade. Increased by economic `ocean_harvest_mult`.
## Ecology & Terrain
**Terrain Quality** — Fertility score per tile (1–5). Determines terrain type and yields.
**Double Buffering** — Read from snapshot, write to new buffer, swap. Prevents order-dependent artifacts.
## Civic System
**4-Axis Model** — Government (ruler selection) × Authority (power justification) × Labor (work organization) × Economy (wealth production/distribution). Religion reserved for expansion. See [civics/OVERVIEW.md](civics/OVERVIEW.md).
**Anarchy Period** — 5-turn penalty when switching any civic axis. Production halved, no gold income. Anarchy government exempts from this.
**Pressured Transition** — Nothing is forced. At inequality ≥50, Gilded Tyranny has no instability cost (others do). At inequality ≥70, Plutocracy has no crisis cost (others do). Player always chooses.
**Exploitation Rate** — Per-tile damage from labor, amplified by economy. `labor.rate × economy.mult`. Labor axis sets the base rate, economy axis multiplies it.
**Capital Siphon** — Percentage of peripheral city surplus flowing to capital. Set by economy axis.
**Savings Rate** — Compound interest on treasury per turn. Set by economy axis (+1% from Oligarchic authority). The rich-get-richer incentive.
## Social Dynamics
**Inequality** — Per-player metric (0–100). Emerges from coefficient of variation of city wealth levels. Risk multiplier, not direct happiness drain. Threshold effects at 10/25/40/50/60/70/80.
**Relative Deprivation** — Per-city happiness based on wealth gap vs capital. `(capital.wealth - city.wealth) / capital.wealth`. Poor city in poor empire = fine. Poor city next to rich capital = fury.
**Suppression** (Nationalism authority) — Halves education awareness effect. Degrades 0.01/turn. After 50 turns at 50% — then accumulated inequality hits.
**Scapegoating** (Nationalism authority) — +3 happiness while at war or with declared enemy. -5 at peace with no enemy. Fascism requires a permanent enemy.
## Victory Wonders
**Doomsday Device** — Mundane evil victory. Destroys global ley network: all ley density → 0, all summons die, all enchantments break, all mana nodes dark. Builder wins because they rejected magic (mundane path). "I don't have to succeed, I just have to be more successful than everyone else."
**Aura Range** — Zone of worker influence. Master workers affect their home tile only. Grandmaster workers affect their home tile (+15% efficiency) and all adjacent tiles (+10%). Auras do not stack — the highest-value aura applies. See [cities/POPULATION.md](cities/POPULATION.md).
**Hybrid Structure** — An irreversible merged building created when two compatible building pairs share a tile and the prerequisite tech (Advanced Synthesis) is researched. Examples: War Academy (Barracks+Rifle Range + Stable+Barding Hall), Assault Citadel (Barracks+Sword Hall + Siege Workshop+Siege Annex). Cannot be un-merged; must be demolished and rebuilt from scratch to undo. See [cities/BUILDINGS.md](cities/BUILDINGS.md).
**Utilization** — The fraction of same-category buildings in a worker's aura range that are actively staffed. Formula: `active buildings in aura range / total same-category buildings in aura range`. High utilization reduces expertise decay: `effective_decay = base_decay × (1 - utilization)`. See [cities/POPULATION.md](cities/POPULATION.md).
**Impact Winter** — Climate penalty following a medium or large asteroid impact. Reduces food yields across the affected biome region for 10–20 turns. See [terrain/VERTICAL_LAYERS.md](terrain/VERTICAL_LAYERS.md).
**Graviton Drive** — Tier-10 research technology. Enables asteroid redirection. Consumed on use (1-use per ship). See [terrain/VERTICAL_LAYERS.md](terrain/VERTICAL_LAYERS.md).
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## Terrain & Engineering
**Tile HP** — Degradation state for surface and underground tiles. Surface states: Normal → Damaged → Cratered → Sunken → Ruins. Underground states: Solid → Stable → Developed → Hollowed → Cracked → Rubble → Sinkhole. See [terrain/TERRAIN_SYSTEM.md](terrain/TERRAIN_SYSTEM.md).
**Structural Integrity** — The tile HP system applied to underground layers. Collapse risk increases as tiles move from Solid to Hollowed. See [terrain/UNDERGROUND.md](terrain/UNDERGROUND.md).
**Excavation** — The process of creating underground space. Queued via Mason Lodge; costs production and stone; time scales with depth (L1=4–6 turns, L2=8–10, L3=12–15). Requires the previous layer to already be excavated. See [terrain/UNDERGROUND.md](terrain/UNDERGROUND.md).
**Raw Cavern** — First underground tile state after excavation completes. Usable but unfinished — can be upgraded to Finished Cavern (habitable) or Developed Chamber (full city functionality). See [terrain/UNDERGROUND.md](terrain/UNDERGROUND.md).
**Controlled Collapse** — Demolitions Expert ability to deliberately trigger underground collapse at a target tile. Used offensively (destroy enemy foundations), defensively (seal infiltration routes), or as a trap. See [units/SPECIALISTS.md](units/SPECIALISTS.md) and [terrain/UNDERGROUND.md](terrain/UNDERGROUND.md).