What guidelines apply to the 3D models' geometries?

• Individual models should have fewer than 5000 polygons each.
• They should never be complex; photo-textures should be used in lieu of geometries where possible.
• Polygons should never have broken vertices, T intersections, spiderweb faces, hidden faces, z-fighting, self-intersections or internal/unseen geometry.
• Individual buildings should be represented by a single group of geometries, not multiple stacked primitives.