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UBC Theses and Dissertations

An evaluation of overviews for large tree navigation Bodnar, Adam Michael


As the amount of information that must be understood by people continues to grow, techniques for efficiently exploring large datasets become increasingly important. Pan and zoom interaction has been shown to be effective for exploring small datasets. However, pan and zoom on its own provides no visual cues about regions of the dataset outside the current field of view, which can result in loss of orientation, leading to inefficient patterns of navigation. Overviews offer one possible solution to this problem by providing the user with contextual information regarding regions outside the current field of view, at the cost of reducing the screen real estate available for the primary detail view, and imposing the need to switch attention between multiple views. Focus+Context techniques offer another solution to this problem by integrating focus and context regions into a single view, often using distortion-based methods, which themselves impose a cost of tracking objects undergoing nonlinear transformations. While overviews have been shown to be beneficial for pan and zoom interfaces, no study to date has explored the potential benefits of adding an overview to Focus+Context interfaces. This thesis presents two studies that evaluate overviews for large tree navigation. Interfaces implementing these techniques were used by 80 subjects, over two studies, to perform a task exploring a large hierarchical tree dataset, which was motivated by the needs of evolutionary biologists. Our first study was designed to investigate the optimal size for an overview for both pan and zoom and Focus+Context interfaces. Our results show that the size of the overview did not affect performance, but the presence of an overview did impact the strategy users adopted. Our second study was designed to compare the performance of pan and zoom and rubber sheet navigation techniques with and without an overview. This thesis also presents the first step towards a taxonomy of tasks for large tree navigation. Our taxonomy is informed from interviews with evolutionary biologists who use large trees to investigate the evolutionary relationships between species. All interfaces implemented guaranteed visibility, a recent innovation in the field of information visualization, which ensures that regions of interest remain visible to the user at all times, independent of navigation actions. We discuss the implications of this research, including the relationship between overviews and guaranteed visibility, and propose directions for future work.

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