Improving user comprehension of Euler diagrams

The graphical choices made when laying out Euler diagrams impact upon both aesthetic quality and comprehensiveness. Graphical choices include the shape, size and colour of closed curves which are commonly described as retinal variables to which we are known to be perceptually sensitive. There is copious literature providing guidance as to how best use retinal variables to visualise both quantitative and qualitative information for a wide range range of diagram types. Further, this guidance is explicitly defined to optimise the users´ comprehension of such information. However, there exists little, if any, literature affording guidance as to how best to use retinal variables when laying out Euler diagrams. Here we present a novel insight as to where retinal variables manifest in Euler diagrams, how they might influence our perception of Euler diagrams and, as a consequence, provide motivation and guidance for establishing layout guidelines.