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Issue No. 12 - Dec. (2011 vol. 17)
ISSN: 1077-2626
pp: 2440-2448
Michael Burch , VISUS, University of Stuttgart
Natalia Konevtsova , VISUS, University of Stuttgart
Julian Heinrich , VISUS, University of Stuttgart
Markus Hoeferlin , VISUS, University of Stuttgart
Daniel Weiskopf , VISUS, University of Stuttgart
Node-link diagrams are an effective and popular visualization approach for depicting hierarchical structures and for showing parent-child relationships. In this paper, we present the results of an eye tracking experiment investigating traditional, orthogonal, and radial node-link tree layouts as a piece of empirical basis for choosing between those layouts. Eye tracking was used to identify visual exploration behaviors of participants that were asked to solve a typical hierarchy exploration task by inspecting a static tree diagram: finding the least common ancestor of a given set of marked leaf nodes. To uncover exploration strategies, we examined fixation points, duration, and saccades of participants' gaze trajectories. For the non-radial diagrams, we additionally investigated the effect of diagram orientation by switching the position of the root node to each of the four main orientations. We also recorded and analyzed correctness of answers as well as completion times in addition to the eye movement data. We found out that traditional and orthogonal tree layouts significantly outperform radial tree layouts for the given task. Furthermore, by applying trajectory analysis techniques we uncovered that participants cross-checked their task solution more often in the radial than in the non-radial layouts.
Hierarchy visualization, node-link layout, eye tracking, user study.

D. Weiskopf, M. Burch, J. Heinrich, N. Konevtsova and M. Hoeferlin, "Evaluation of Traditional, Orthogonal, and Radial Tree Diagrams by an Eye Tracking Study," in IEEE Transactions on Visualization & Computer Graphics, vol. 17, no. , pp. 2440-2448, 2011.
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