> Manhole covers are round if they cover a pipe and square if they cover a brick built manhole

This is inaccurate as a generalization - in the three jurisdictions I've worked in, they're round if they're newer than ~1990, and mix of round and square (or two triangles that go together to make a square) if they're older than that. The frame and cover are replaced independently from the MH structure itself so the cover doesn't tell you anything about the makeup of the structure.