In this project, we examined ways to help present/depict hierarchical (tree) information structures in order to help people understand them and access the data in them. The Treemap visualization technique developed by Ben Shneiderman and Brian Johnson at Maryland is a well-known technique for depicting hierarchies. It uses a rectangular, space-filling slice-and-dice technique to visualize objects in the different levels of a hierarchy. The area and color of each item corresponds to an attribute of the item as well.
The SunBurst technique is an alternative, space-filling visualization that uses a radial rather than a rectangular layout. In SunBurst, items in a hierarchy are laid out radially, with the top of the hierarchy at the center and deeper leves farther away from the center. The angle swept out by an item and its color correspond to some atttribute of the data. For instance, in a visualization of a file system, the angle may correspond to the file/directory size and the color may correspond to the file type. An example Sunburst display is shown below.
In one study, we compared use of SunBurst to use of a Treemap. We created two UNIX file/directory browser tools that use the Treemap and SunBurst visualization techniques, respectively. We then used the two tools in an experiment in which 60 students performed a series of typical file/directory-related tasks. We measured both correct task completion rates and time to complete the tasks.
Results of the study appear in a technical report and in an article in the International Journal of Human-Computer Studies, both listed above. In general, the participants preferred the Sunburst tool, primarily due to its more explicit portrayal of the hierarchy structure. We found that performance with the Treemap tool benefited when a participant used the Sunbust tool earlier, suggesting a learning effect. Performance with both tools, in terms of correct task completions and times, was relatively comparable on a "small" hierarchy consisting of about 500 files. Performance on a "large" hierarchy of about 3000 files favored the Sunburst, particularly when comparing initial uses of each tool.
In another research effort, we developed a series of techniques for helping viewers to examine the small, peripheral files that often appear in a SunBurst display when it shows many files. The three techniques we developed are called Angular Detail, Detail Inside and Detail Outside. All use smooth animation and a focus context display methodology to help present small files for close examination within the context of an overview of the entire hierarchy. An article at InfoVis 2000 and a technical report, both listed above, describe this research. To most clearly understand the techniques, view a 4-minute video that we prepared for the InfoVis 200 Conference. 40 megabyte MPEG video.
