Fine large navigational chart of the Southwestern United States, locating VOR airway beacons.
The map includes instructions and "Rules for Correction to Radio Bearings From Plane To Station."
On the Lambert Conformal Conic Projection.
Very high frequency omni-directional range (VOR) is a type of short-range radio navigation system. VOR enables aircraft to determine position and maintain a course by receiving signals transmitted by a network of ground radio beacons. Developed in the United States beginning in 1937, VOR was deployed by 1946 and became the standard air navigational system in the world until the advent of satellite / GPS systems in the 21st Century.