Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Interaction <s> The traditional approach to representing tree structures is as a rooted, directed graph with the root node at the top of the page and children nodes below the parent node with lines connecting them (Figure 1). Knuth (1968, p. 305-313) has a long discussion about this standard representation, especially why the root is at the top and he offers several alternatives including brief mention of a space-filling approach. However, the remainder of his presentation and most other discussions of trees focus on various node and edge representations. By contrast, this paper deals with a two-dimensional (2-d) space-filling approach in which each node is a rectangle whose area is proportional to some attribute such as node size. <s> BIB001 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Interaction <s> Big information worlds cause big problems for interfaces. There is too much to see. They are hard to navigate. An armada of techniques has been proposed to present the many scales of information needed. Space-scale diagrams provide an analytic framework for much of this work. By representing both a spatial world and its different magnifications explicitly, the diagrams allow the direct visualization and analysis of important scale related issues for interfaces. <s> BIB002 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Interaction <s> A variety of information visualization tools have been developed recently, but relatively little effort has been made to evaluate the effectiveness and utility of the tools. This article describes results from two empirical studies of two visualization tools for depicting hierarchies, in particular, computer file and directory structures. The two tools examined implement space-filling methodologies, one rectangular, the Treemap method, and one circular, the Sunburst method. Participants performed typical file/directory search and analysis tasks using the two tools. In general, performance trends favored the Sunburst tool with respect to correct task performance, particularly on initial use. Performance with Treemap tended to improve over time and use, suggesting a greater learning cost that was partially recouped over time. Each tool afforded somewhat different search strategies, which also appeared to influence performance. Finally, participants strongly preferred the Sunburst tool, citing better ability to convey structure and hierarchy. <s> BIB003 </s> Hierarchical Aggregation for Information Visualization: Overview, Techniques, and Design Guidelines <s> Interaction <s> Radial, space-filling (RSF) techniques for hierarchy visualization have several advantages over traditional node-link diagrams, including the ability to efficiently use the display space while effectively conveying the hierarchy structure. Several RSF systems and tools have been developed to date, each with varying degrees of support for interactive operations such as selection and navigation. We describe what we believe to be a complete set of desirable operations on hierarchical structures. We then present InterRing, an RSF hierarchy visualization system that supports a significantly more extensive set of these operations than prior systems. In particular, InterRing supports multi-focus distortions, interactive hierarchy reconfiguration, and both semi-automated and manual selection. We show the power and utility of these and other operations, and describe our on-going efforts to evaluate their effectiveness and usability. <s> BIB004
Beyond uniform methods for aggregation and rendering, one of the main benefits of hierarchical aggregated visualizations is that they can be made to support the same set of basic interaction techniques for navigating and manipulating the aggregate hierarchy. This allows users to apply the same reasoning and interaction strategies to different visualization techniques that support hierarchical aggregation. Here, we will discuss a basic set of common interaction techniques for this purpose. Note that while this paper mainly focuses on developing new visualization techniques that support hierarchical aggregation, the space is also open for designing new interaction techniques for interacting with them. Hopefully, the presentation here will also serve as a useful framework for such activities. For each of the interaction techniques in this section, we will use a combination of space-scale diagrams BIB002 and the aggregate hierarchy to describe the mechanics of the interaction. We will also give concrete examples of each interaction in existing systems and techniques. Because these interaction techniques mainly deal with various ways of navigating hierarchies (which is what an aggregate tree actually is), many of these techniques can also be found in tree visualization tools like treemaps BIB001 , Sunburst BIB003 , and InterRing BIB004 .