The data here is something like the inverse of a price index (which takes low values where prices are lower).
N.B. Normally, you might see something like this with “heat map” shading. The problem with that is that the color blind have difficulty with that choice of colors. The use of blue-to-yellow here may not seem that comfortable, but it has the virtue that even the color blind can readily see the differences.
Anyway, blues are bad: stuff is expensive there and $100 doesn’t go as far. Yellows are better: your $100 will buy more there. The biggest difference, going from Mississippi to D.C., is 37%. So at the store, you’d walk out with a third more loot.