Summary
A design pattern in which players have no information about areas of the game world that are not currently being observed or have not yet been explored. Fog of War is the principal mechanism for creating spatial information asymmetry — it transforms geographic knowledge into a resource that must be actively acquired (Björk & Holopainen 2004, see source-patterns-in-game-design).
The key design tension: Fog of War generates exploration goals and asymmetric information naturally, but it conflicts with Consistent Reality Logic (players in most games have more than one set of eyes, and the fiction of limited sight must be accepted).
Implementation
Two primary design decisions:
-
Shared or individual fog — Is the unexplored area hidden from all players equally (symmetric fog, e.g. board game tile-laying), or does each player see only what their own units can observe (individual fog, e.g. StarCraft)?
- Shared fog: simpler, common in physical games using face-down tiles
- Individual fog: creates asymmetric information and enables stealth, deception, and meaningful decisions about reconnaissance investment
-
Permanent or returning fog — Once an area is explored, does it stay revealed, or does the fog return?
- Permanent reveal: encourages initial exploration; reduces memorisation load
- Returning fog: does not show enemy unit movement through previously seen areas unless currently observed; encourages ongoing reconnaissance and guard missions; promotes memorisation
Observation mechanics:
- Fog clears based on the movement and observation ranges of Avatars or Units
- Different unit types can have asymmetric observation ranges — a scout clears more fog than a tank; this creates intransitive trade-offs between combat power and information gathering
- Games using Game State Overview (minimap) typically apply fog at the same level as the game world view
Partial fog variants:
- Reveal terrain but hide unit positions — players know the map layout but not where enemies currently are (most RTS games)
- Reveal specific information while hiding others — Metroid Fusion shows room layout and power-up locations on the map but not their precise in-room position, creating a targeted search goal
Physical implementation:
- In board games: face-down tiles revealed on entry (Tile-Laying); exploration tokens; hidden unit placement
Trade-offs
| Design choice | Benefit | Risk |
|---|---|---|
| Individual fog | Asymmetric information; strategic depth | Complexity; harder to implement in physical games |
| Returning fog | Ongoing reconnaissance value; tension | Cognitive load; frustration with backtracking |
| Permanent reveal | Simple; no memorising burden | Exploration value is one-shot; no sustained tension |
| Partial fog (terrain revealed, units hidden) | Balance of orientation and uncertainty | May feel arbitrary to players unfamiliar with the convention |
Critical tension: Fog of War is a prerequisite for Secret Resources and asymmetric information in spatial games. Without some form of information hiding, all spatial strategy collapses toward perfect-information play where geographic advantage is immediately known to all parties. This is appropriate for some games (Chess) but eliminates a major category of meaningful-decisions.
Examples
- StarCraft / StarCraft II — individual returning fog; reconnaissance is a distinct strategic investment; Dark Templar (invisible units) exploit the fog systematically
- Civilisation series — players begin knowing only the immediate surroundings of their starting units; exploration and territorial knowledge are core early-game resources
- Metroid Fusion — partial fog on the Game State Overview; reveals room layout and power-up zone but not exact in-room position, creating Exploration goals within already-mapped areas
- Battleship — the canonical physical Fog of War; each player’s grid is hidden; attacks are information probes
- Fog of War in tabletop RPG — the Game Master’s screen as physical Fog of War; only revealed when the GM narrates or players investigate
Related
exploration | asymmetric-information | reconnaissance | stealth | meaningful-decisions | game-theory-fundamentals | randomness-in-games | paper-rock-scissors | balancing-effects | source-patterns-in-game-design