Isopleths

Isopleths - simplifies and generalizes data with a continuous distribution and shows it as a third dimension on a map.

http://dwb4.unl.edu/chem/chem869v/chem869vlinks/weather.about.com/newsissues/weather/library/weekly/aa071600a.htm
http://dwb4.unl.edu/chem/chem869v/chem869vlinks/nadp.sws.uiuc.edu/isopleths/maps1998/so4.gif