Maybe it's just that I can see San Francisco Bay out my window. But I can't visualise the whole of the world's oceans, nor can I visualise a swimming pool coat

Maybe it's just that I can see San Francisco Bay out my window. But I can't visualise the whole of the world's oceans, nor can I visualise a swimming pool coated with half a mile of oil. But a thin layer of oil all across the Bay, that I can easily imagine.