Mathematical Theory of the Mercator Map

Because of the attention which the Mercator projection has recently received in the press, the manner in which this map is used by the navigator is doubtless familiar to a large section of the public. The projection owes its importance to the fact that the rhumb line direction between two points on the earth can be found by drawing a straight line between the corresponding points on the map, and measuring the angle at which the line intersects the meridians of the map.