Abstract
The Treemap is one of the most relevant information visualization (InfoVis) techniques to support the analysis of large hierarchical data structures or data clusters. Despite that, Treemap still presents some challenges for data representation, such as the few options for visual data mappings and the inability to represent zero and negative values. Additionally, visualizing high dimensional data requires many hierarchies, which can impair data visualization. Thus, this paper proposes to add layered glyphs to Treemap’s items to mitigate these issues. Layered glyphs are composed of N partially visible layers, and each layer maps one data dimension to a visual variable. Since the area of the upper layers is always smaller than the bottom ones, the layers can be stacked to compose a multidimensional glyph. To validate this proposal, we conducted a user study to compare three scenarios of visual data mappings for Treemaps: only Glyphs (G), Glyphs and Hierarchy (GH), and only Hierarchy (H). Thirty-six volunteers with a background in InfoVis techniques, organized into three groups of twelve (one group per scenario), performed 8 InfoVis tasks using only one of the proposed scenarios. The results point that scenario GH presented the best accuracy while having a task-solving time similar to scenario H, which suggests that representing more data in Treemaps with layered glyphs enriched the Treemap visualization capabilities without impairing the data readability.
Highlights
The Treemap is an information visualization (InfoVis) technique that uses recursive areal subdivision to visualize hierarchical data organized in tree structures [1]
We present two study categories that influenced this work: studies on glyphs applied in several InfoVis techniques, and studies about the use of glyphs in Treemaps
Considering the analysis of correct answers and time average of the T2, T3, T4, T5 e T6 tasks, we can confirm the hypotheses Hypothesis 2. (H2), Hypothesis 3. (H3), Hypothesis 4. (H4), and Hypothesis 5. (H5), i.e., the combination of hierarchies and layered glyphs is suitable for search tasks
Summary
The Treemap is an information visualization (InfoVis) technique that uses recursive areal subdivision to visualize hierarchical data organized in tree structures [1]. Considering the Treemap challenges, the potential of glyphs to represent multidimensional data, and the lack of studies and evaluations about glyphs in Treemaps [10], this work presents a prototype that adds configurable layered glyphs in visual Treemap items to mitigate the squarified Treemap challenges. With this approach, the Treemap can represent more multidimensional data, including options to encode small, zero, and negative values.
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