Jersey 394

     An isoline map is a map with continuous lines joining points of the same  value. Examples would be equal altitude (contour lines), temperature (isotherms), barometric pressure (isobars), wind speed (isotachs), wind direction (isogon), wind shear (isoshear), etc. Isoline mapping is used to interpret the information on some thematic maps. In 1584 Peter Bruinss drew a chart with lines showing equal depths of water. This may be the first isogonic chart, but it was not published.
     In 1701 Edmond Halley published the first such map, a chart of the Atlantic Ocean showing lines of magnetic deviation. A year later he published a map showing isogones over the whole world. In Halley's time the lines were called Halleian lines in recognition of Halley's contribution.

Norway 839

     In 1819 Christopher Hansteen published a volume of researches on terrestrial magnetism. He established the first astronomical observatory in Norway, and was appointed President of the Geodetic Institute. A crater on the moon is named for him.
     The stamp shows a map of the world (Mercator projection) with generalized lines of magnetic declination