This atlas documents the system dynamics in the Micropolis simulation engine — the GPL source of the original SimCity (1989). Every diagram was reverse-engineered from src/sim/s_*.c in the osgcc/simcity repository. Arrows are code paths; labels are C function names, constants, and thresholds governing each transition.

The simulation runs on a 120×100 tile map. Each tick, Simulate() executes one of 16 phases in round-robin: phase 0 advances the clock and recomputes demand valves; phases 1–8 scan the map in 15-column strips; phases 9–15 handle census, taxes, power, pollution, crime, population density, fire coverage, and disasters.