Isopach Map

http://www.southampton.ac.uk/~imw/Durlston-Bay-Lower-Purbeck.htm

Above shown is an example of an Isopach map, this map type is utilized for illustrating thickness variations within a certain area. Isopach lines are a type of contour line,  this map type is most commonly used for hydrographic surveys, stratigraphy, sedimentology and structural geology uses.  This map is showing the thickness of the southern part of England's English Chanel. As in relation with maps that use contour lines, the closer concentration of lines depict a larger amount of thickness.