This picture shows Mercator's idea of the Arctic. In the center, at the North Pole, there was supposed to be a place where water poured into the center of the Earth. It was fed by four great rivers. If ships ventured too far, they would be unable to escape and would be sucked down into the Earth. Too bad there is no "artist's rendering" of the hapless sailor's plight as their ship is sucked under. Mercator's projection can't show the North pole as it projects to "the point at infinity". It's curious that Mercator imagined some kind of physical "singularity" there too, that would suck ships down.