Isopleths

Source: http://dwb4.unl.edu/Chem/CHEM869V/CHEM869VLinks/weather.about.com/newsissues/weather/library/weekly/aa071600a.htm

Isopleths are maps have too, have contour lines drawn through to measure equal data. This map is a Isopleth map that represents the Hydrogen Ion concentration as pH from measurements made at the field laboratories in 1998. The scale states that red is < 4.3 level and green is >5.3. That being said, the east, which is mostly red has a lower lever than the west, which is green.