The polyconic projection was used for most of the earlier USGS topographic quadrangles. The projection is based on an infinite number of cones tangent to an infinite number of parallels. The central meridian is straight. Other meridians are complex curves. The parallels are non-concentric circles.
Scale is true along each parallel and along the central meridian.
Azimuthal Projections Azimuthal Equidistant Azimuthal equidistant projections are sometimes used to show air-route distances. Distances measured from the center are true. Distortion of other properties increases away from the center point. The Lambert azimuthal equal-area projection is sometimes used to map large ocean areas. The central meridian is a straight line, others are curved.