Visualizing Dynamic Weighted Digraphs with Partial Links

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Partial links for dynamic weighted digraphs for migration data

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Graphs are traditionally represented as node-link diagrams, but those typically suffer from visual clutter when they become denser, i.e. more vertices and edges are present in the data set. Partial link drawings have been introduced for node-link diagrams aiming at reducing visual clutter caused by link crossings. Although this concept has been evaluated as performing well for some parameter settings it has not been used for visually encoding dynamic weighted digraphs. In this paper we investigate the problem of visualizing time-varying graphs as one node-link diagram in a specific layout by exploiting the links as timelines. Partially drawn links are used to show the graph dynamics by splitting each link into as many segments as time steps have to be represented. Conventional 2D layout algorithms can be applied while simultaneously showing the evolution over time. Color coded tapered links represent the changing weights which reduce possible overlaps at the link target nodes when traditional arrow-based directed links would be used instead. We experiment with different graph layouts as well as with differently large data dimensions, i.e. number of vertices, edges, and time steps. We illustrate the usefulness of the technique in a case study investigating dynamic migration data.

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