Speaking of petty... plans are two-dimensional representations of a horizontal cut of a building's interior or of its site. Exteriors are not represented in plan (they are represented in elevations), and even if they were, they could neither be "cylindrical" nor "spherical," as those are three-dimmensional objects, and plans, as I already said, are two-dimensional representations. Having said all of that,the exterior shape of the Gugenheim is not a cylinder. It is more like a cone whose tip has been lopped off.