The 1950 world isogonic chart

Under a working agreement with the United States Navy Hydrographic Office, a 1950.0 edition of the isogonic chart of the world has been compiled by the United States Coast and Geodetic Survey. Data were collected from all available sources throughout the world. These data were punched into cards, reduced to epoch 1950.0, sorted and averaged by one-degree quadrangles, using machine processes. The average values so derived were entered on base maps and used to control the drawing of isogonic lines. The method has resulted in a saving of many man-years of hand work. The results have been published on one mercator and two polar charts by the Hydrographic Office.