30. Continuously variable proportional circle map

https://www.e-education.psu.edu/geog486/book/export/html/1796

A continuously variable proportional circle map uses varying circles that contain values that are continuous. Unlike proportional circle map, the circles values are not just in a range of values, but rather a specific value. This map of France is dated  back to 1850s, which was when proportional circles were first used on a map proportional to the values that are being mapped. The creator shows how the proportion of meat that were sent to Paris butcheries from different regions across France.