This is a chloropleth (a political map shaded by some other variable). It shows which counties had median income go up or down from 2007 to 2012.
We talk about recessions as if they’re national, but that’s only in an average sense. From this, it’s apparent that the Great Recession was mostly the southwest, the southeast, and some areas in the orbit of major cities: Detroit, Chicago, New York, Philadelphia, Seattle.
Do note the green region: this is the oil boom in the northern plains.