19 Of course, on a single sheet can be drawn map of the entire surface of the Earth. However, the points located on the edge of a map will be displayed correctly: some of their neighborhoods would be "beyond the edge", on the other side of the sheet. You can fix this by continuing the card a little "over the edge" (cartographers so often do), but from a mathematical point of view, it would be incorrect, because some points are shown on the same card twice. This problem is solved by the creation of the atlas. atlas maps overlap, and because each point of the Earth for at least one card is depicted together with the surrounding area. And at the same time in the atlas no points that would fall on the same card twice. The number of cards may be different, but the mathematical theory of smooth manifolds proves that the spherical surface of the Earth atlas must contain at least two cards, and the satin surface of a torus - four.