Gnomonic Projection

A map projection formed by projecting the Earth’s surface from its centre onto a tangent plane.

Every great circle appears as a straight line, making the projection useful for planning the shortest route on a spherical Earth. Scale and shape distortion grow rapidly away from the tangent point, and only less than one hemisphere can be represented.

A great-circle route planned on a gnomonic chart is commonly transferred as a series of waypoints to a Mercator or electronic chart for practical navigation. The straight line is not automatically safe or optimal once land, weather, traffic, currents and ellipsoidal calculations are considered.