Z-fighting

The depth buffer stores one number per pixel saying how far away the winning surface was. When two surfaces land on effectively the same number, rounding decides the winner, and rounding changes as the camera moves. The result is that crawling stripey shimmer across a floor decal, a sticker on a car body, or two walls modeled in the same plane.

The usual culprit is not the geometry, it's the camera. Depth precision is not linear: after the perspective divide the stored values fall off hyperbolically with distance, so almost all of the precision gets spent between your near plane and a short way past it. (Logarithmic depth is a different technique, covered below, not how ordinary perspective depth behaves.) A camera with near 0.001 and far 100000 has essentially no precision left at 50 units out. Push the near plane out as far as your scene tolerates before touching anything else, it is the single biggest win. Then pull the far plane in.

Fixes for the geometry itself: separate coplanar faces by a small real offset instead of stacking them; use polygon offset (polygonOffsetFactor / polygonOffsetUnits) to nudge decals toward the camera in depth only; delete hidden interior faces that duplicate an outer wall. Logarithmic depth buffers exist and help on planet-scale scenes, but they cost performance and break some post effects, so treat that as the last resort, not the first move.