Continuously variable proportional circle map

http://content.cdlib.org/xtf/view?docId=kt4j49n6r5&brand=calisphere&doc.view=entire_text

The above map is an example of a continuously variable proportional circle map because it is able to convey data about an area, but does with the use of varying circles that relate to the relative occurrence. In this exact map, the map represents data that has been gathered from different amounts of plankton throughout an area in California. This map is really helpful for many reasons, one of which being the fact that because there are no ranges, it is easier to see more of the "exact" amount of a certain factor in different parts of one subject. This trend is very helpful if one is trying to see more of a pattern or to track the specific changes within a characteristic and therefore see the "little" details and how it can affect the overall outcome.