Gnomonic Chart. Chart constructed by gnomonic projection. All British Admiralty charts on scale of 1/50,000 or smaller are gnomonic. Charts of polar area are nearly always gnomonic.
Gnomonic Projection. Projection of Earth's surface on a plane that is tangent to surface at a given spot, and by lines from centre of Earth. Advantages are (1) So long as area is small there is no appreciable distortion: (2) projection of great circles are straight lines: (3) there is little distortion in polar regions. Its disadvantage is that scale is not constant; areas away from point of tangency are distorted.