Fog of War

Terrain stays hidden until visited, and once explored it often persists as a remembered snapshot that no longer updates, so a base seen ten minutes ago may be a lie. Units project a vision radius that travels with them. Everything outside it is unknown: enemy positions, army composition, expansions. Producing vision therefore costs resources, and denying it, through terrain, cloaking or high ground, becomes a tactic in its own right.

Westwood Studios used the mechanic in Dune II in 1992 as the real-time strategy template took shape, though hidden-map play was already familiar from earlier computer wargames and from the board wargames those descended from. Necessity helped. An opponent whose entire build is visible gives nobody a reason to scout, and a real-time game with perfect information collapses into arithmetic. Concealment also flatters simple artificial intelligence by hiding its behaviour.

Scouting, deception and the timing attack all descend from this one restriction, and it is why strategy games have a metagame at all. Costs fall on spectators and newcomers, who cannot see why a player is suddenly panicking, and on interface designers, who must communicate absence. Cheats that reveal the map are so destructive precisely because the entire genre rests on the assumption that knowledge is expensive.