Rhumb lines keep a steady bearing on a curved Earth

A rhumb line, also called a loxodromic course, crosses the curved surface of the Earth on a constant bearing. Holding that fixed course can make steering practical for a sailing vessel even though the resulting path is not the shortest route between two points. On a globe, continuing along such a bearing produces a curving or spiralling track rather than the straight line suggested by a flat map. The method still has to be calculated, but its operational advantage is that the helmsman can maintain a steady course. This comparison prepares the viewer for the more mathematically demanding great-circle alternative.