As an American, I've never seen more than maybe 2-3 football fields next to each other. They're usually stand alone items so that is even rare. Imagining them in plural at all is something people likely do with a large degree of error is my guess, even for us American's that are familiar with the size of a single field. It's a awfully small unit for anything related to space. Even a kilometer which is ~11x as long as an American football field is a small unit for space.