Isogonic map

Historical isogonal map from 1860

An isogon map is a map that shows the location of a magnetic compass ( declination ) using isolines ( isogons , lines of the same location). The deviations vary from place to place in the world. Isopores are occasionally also entered in these maps , i. H. Isolines with the same annual change in magnetic declination.

Isogonal maps are geophysical maps.

Web links

• http://www.geo.fmi.fi/MAGN/igrf/ Isogenenkarte - create it yourself (Java applet) engl.
• http://historicalcharts.noaa.gov/historicals/preview/image/3077-00-1946 Isogonic Chart for 1945 United States Including Isoporic Lines (Engl.)
• http://phrontistery.info/contour.html Forthright's Phrontistery (engl.)