A diagram with a set of consecutive circles of equal area is depicted in Leonardo da Vinci’s Codex Atlanticus 221v-b, a technique later deployed by the engineer Augustin-Jean Fresnel. Circles have been used as part of data visualisations for centuries. Circular heatmaps often contain zones with unequal areas, however, which can distort the data. Drawing on Fresnel’s circles, the Fresnel Chart is a form of circular heatmap in which each zone is equal in terms of area. Although the diagram itself is not new, here I propose a new term to describe the technique.

Illustrative example of the Fresnel Chart using a random dataset.