Gnomonic chart

A gnomonic chart is a projection drawn from Earth’s center onto a tangent plane, with the defining property that every great circle plots as a straight line. The navigator uses it to plan a great-circle track: join the two points with a ruled straight line, read off intermediate latitudes and longitudes, then transfer those waypoints to a Mercator chart where the route appears as a series of rhumb-line legs. Scale and shape distort badly away from the point of tangency, so gnomonic charts are not used for plotting a fix. Polar charts often use the gnomonic projection for the same straight-line great-circle benefit.