The New Isogonic Chart of the United States

The discussion explains some of the factors affecting the production of isogonic charts, and presents a comprehensive plan which is expected to promote uniform standards of treatment for future work. The scheme used for the chart for 1940 is outlined as a modification of that plan, designed primarily to correlate that chart with the previous (1935) one. The behavior of secular change as reflected in the new chart is discussed» and the use of shading in a way not previously employed in this series of charts is also explained.