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. In Halley's time the lines were called Halleian lines in recognition of Halley's contribution. A year later Halley published a map showing isogones over the whole world.

     Perhaps the most common isoline map is one which shows lines indicating equal elevation, a contour map.