Isoleth Map

http://www.flutrackers.com/forum/showthread.php?t=132504

Above is an example of an Isopleth map, this map type uses lines joining points of an equal value to show variations in that value e.g. contour lines on a topographical map, isobars on a weather map.  This map is not strictly confined to weather uses, for example this Isopleth map is conveying the amount of deaths in California as a result of the H1N1 virus in 2009.  The darker shaded regions represent the higher death toll where the lighter shaded regions represent the lower death toll regions.