Perimeter's central mechanic is terraforming. The use of a "paintbrush" tool allocates where land should be raised, lowered, or flattened, and in the process deploys swarms of automated bulldozer-like machines to perform the player's bidding. They'll collect "sponge" (the material of the world) until full then empty their load at some other location, creating a tiny mound. What makes the terrain so convincingly malleable is the game's voxel engine, which basically replaces traditional polygons with cubes. These voxels give the land a sandy Play-doh look, which complements the game's abstract art design.
Terraforming has gameplay consequences. Buildings can only be placed on flat ground; cracking ground underneath buildings will severely damage them. Units can be destroyed by digging pitfalls, while special units can burrow underground to avoid turrets, etc.
Buildings and units are composed of traditional polygons. Units consist of three basic units and are extremely weak. These base units, however, can be combined in an assortment of ratios to yield stronger units. Advanced units can even reform into other units on the fly, allowing for quickly adaptable strategies.
The main storyline follows three human factions traveling through the "Great Chain", a web of parallel dimensions. Unfortunately, each world is infested with the mysterious Scourge, a force capable of assuming the forms of the humans' fears.
Each faction seeks to find peace in this inhospitable multiverse. The Exodus seeks a fabled eden at the end of the Great Chain, the Harkback believes answers lie at their ancestral home at the beginning of the Chain, and the Empire seeks to dominate the Scourge through brute force.
CriticismPerimeter was one of the more innovative real-time strategy games of 2004. Some argue that these innovations pushed the genre forward, while others argue they were merely gimmicks that promoted broken gameplay. Lackluster artificial intelligence is another point of contention.