> 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.
Not quite true. The cover itself has to be supported by a structure. The frame itself is insufficient. If you put a round cover on a square hole it would cave in if a truck ran over it.
> Your note about them not falling in makes me wonder if Google had a different answer?
It's the kind of question that's asked in interviews because it has several answers and a good candidate should be able to think it through and suggest a reasonable number of them and demonstrate their ability to creatively think through a problem. That round covers can't fall in seems one of the simplest and most important, given that a cover that falls in could kill or seriously injure a worker.
Your note about them not falling in makes me wonder if Google had a different answer?