Kasper Hornbaek, Benjamin Bederson, Catherine Plaisant
Information spaces such as maps, desktops, hierarchies, and networks commonly consist of thousands or millions of objects. Graphically displaying such information spaces and developing efficient ways of letting users interact with them are the main challenges of information visualization.
Coordinated overviews and zoomable user interfaces (ZUIs) are two prominent concepts in information visualization. User interfaces incorporating an overview show the details of an information space coordinated with an overview of the entire information space. Experiments have shown that overviews can make users more efficient and satisfied. A zoomable user interface organizes information in space and scale and uses zooming and panning as its main interaction techniques. The reader may find examples of ZUIs in the toolkit Jazz (www.cs.umd.edu/hcil/jazz). Both overviews and ZUIs have been used to display very large information spaces; however, we do not know much about the usability of ZUIs or whether an overview is useful in a ZUI. Will users lose their orientation in ZUIs? Will users recall more information after using a ZUI with an overview? How do different information spaces affect the way users navigate with ZUIs? To address those questions, this paper compared, through an experiment, the usability of zoomable user interfaces with and without an overview and investigated how interface and organization of information space affect how users navigate.
In the experiment, 32 users solved tasks on two maps of American states using ZUIs with and without an overview. Objects on one map were all showed at the same small size; the other map used semantic zooming to make important objects larger than less important ones. Our experiment suggests a trade-off between subjective satisfaction and task completion when providing an overview. Contrary to previous research, we found that the overview with semantic zooming slowed users down. Despite being slower, users preferred having the overview. We conjecture that the map with semantic zooming is more effective because it is organized in multiple levels that might provide an implicit overview. The combination of that map and the interface without an overview also improves users' recall of objects on the map. Our results highlight the influence of the organization of information spaces on usability. Independently of whether users had an overview, they preferred the map with semantic zooming and were significantly faster at completing tasks using that map.
The paper suggests four general usability problems with overviews and ZUIs. First, navigation interaction is often different in the overview and in detail views, causing users problems. Second, small overviews make it difficult for users to navigate precisely; however, large ones take up too much of the screen. Third, clearer and more intuitive interaction techniques for zooming and panning are needed. Fourth, ZUIs without overviews need to better integrate navigation cues within the detail view, to give users some of the satisfaction and confidence found with overviews.
In conclusion, common expectations about difficulties with ZUIs and the utility of an overview were challenged in this paper. The paper stresses that information visualization still raises significant questions, including how users shift attention between different views and how information spaces are most efficiently organized.
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