A case study in fitting area-proportional euler diagrams with ellipses using eulerr

Euler diagrams are common and user-friendly visualizations for set relationships. Most Euler diagrams use circles, but circles do not always yield accurate diagrams. A promising alternative is ellipses, which, in theory, enable accurate diagrams for a wider range of input. Elliptical diagrams, however, have not yet been implemented for more than three sets or three-set diagrams where there are disjoint or subset relationships. The aim of this paper is to present eulerr: a software package for elliptical Euler diagrams for, in theory, any number of sets. It fits Euler diagrams using numerical optimization and exact-area algorithms through a two-step procedure, first generating an initial layout using pairwise relationships and then finalizing this layout using all set relationships.