  Points of interest on a map such as restaurants, hotels, or subway stations,
give rise to categorical point data: data that have a fixed location and one or
more categorical attributes. Consequently, recent years have seen various set
visualization approaches that visually connect points of the same category to
support users in understanding the spatial distribution of categories. Existing
methods use complex and often highly irregular shapes to connect points of the
same category, leading to high cognitive load for the user. In this paper we
introduce SimpleSets, which uses simple shapes to enclose categorical point
patterns, thereby providing a clean overview of the data distribution.
SimpleSets is designed to visualize sets of points with a single categorical
attribute; as a result, the point patterns enclosed by SimpleSets form a
partition of the data. We give formal definitions of point patterns that
correspond to simple shapes and describe an algorithm that partitions
categorical points into few such patterns. Our second contribution is a
rendering algorithm that transforms a given partition into a clean set of
shapes resulting in an aesthetically pleasing set visualization. Our algorithm
pays particular attention to resolving intersections between nearby shapes in a
consistent manner. We compare SimpleSets to the state-of-the-art set
visualizations using standard datasets from the literature.
