Univariate Choropleth Map

The above image, taken from wcr.sonoma.edu/v07n1/20/drugmarkets.html, shows the block-by-block crime propensity in Portland, Oregon. This particular image uses a 4-class system and uses each block as an isolated geographic area. Notice that the classes are not equal. The creator used some other system to design the class scheme used here. With the information provided, we do not have a way of determining what end this has in the depiction.