Animated 2D Visualization of Evolving Trees : A Temporal Treemap Approach

Sammanfattning: Time-dependently changing hierarchical data structures are commonly visualized with animated treemaps. Changes in the data structure produce correlated changes in the animation. While previous treemap animations exclusively consider hierarchical data where only the size of the data points are time-dependently changing, we present a novel method for animating treemaps where the hierarchy of the data structure is also evolving. A change in the hierarchy is referred to as a topological event of the animated treemap. Furthermore, animation stability is a quantitative indicator as to the visual quality of treemap animations. With the proposed method, the stability of animated Slice-and-Dice treemaps is maximized during topological events. Thus, the method produces topologically evolving Slice-and-Dice treemap animations of high visual quality. Inspiration for the proposed method was largely drawn from Köpp and Weinkauf’s recent work on the ordered visualization of time-dependently evolving nested graphs. The research question regarded whether their treemap method for spatially ordering hierarchical data could be translated to the 2D treemap space, in order to optimize the stability of animated Slice-and-Dice layouts. This study does not only report on the development of the proposed method, but also present an accompanying experimental evaluation. While evidence show that the proposed method is incapable of entirely mitigating decreasing stability scores, caused by any possible topological event in an evolving Slice-and-Dice hierarchy, the success of the proposed method has been proven for the most frequent topological events.