Radial Edge Splatting for Visualizing Dynamic Directed Graphs

We describe and discuss a novel radial version of a scalable dynamic graph visualization. The radial layout encodes dynamic directed graphs on narrow rings of a circle. The temporal evolution of the graph is mapped to rings that grow outward from the center of the circle. Graph vertices are placed equidistantly at the borderlines of each ring. Graph edges are displayed as curved lines starting from a source on the inner borderline of the ring and pointing to a target on the outer borderline. To better perceive link directions and structures of large datasets, visual clutter is reduced by exploiting an edge splatting approach that generates density fields of the displayed edges. The radial layout emphasizes newer graphs, displayed in the larger, outer parts of the circle. As a benefit, edge lengths are reduced in comparison to the non-radial visualization. Moreover, the radial layout guarantees the symmetry of the visualization under shifting of vertices. We illustrate the usefulness of the diagrams by applying them to call graph data of the open source software project Cobertura.