Index Value Plot

http://waterwatch.usgs.gov/index.php?id=real&sid=w__plot&r=nc

An index value plot is similar to a line plot but instead of absolute values, data is plotted as an index as the name suggests. In this map, we can see the average stream flow in North Carolina over a period of 45 days on a wet/dry scale with 1 being the driest and 7 being the wettest.