Physical and tangible information visualization

Visualizations in the most general sense of external, physical representations of information are older than the invention of writing. Generally, external representations promote external cognition and visual thinking, and humans developed a rich set of skills for crafting and exploring them. Computers immensely increased the amount of data we can collect and process as well as diversified the ways we can represent it visually. Computer-supported visualization systems, studied in the field of information visualization (infovis), have become powerful and complex, and sophisticated interaction techniques are now necessary to control them. With the widening of technological possibilities beyond classic desktop settings, new opportunities have emerged. Not only display surfaces of arbitrary shapes and sizes can be used to show richer visualizations, but also new input technologies can be used to manipulate them. For example, tangible user interfaces are an emerging input technology that capitalizes on humans' abilities to manipulate physical objects. However, these technologies have been barely studied in the field of information visualization. A first problem is a poorly defined terminology. In this dissertation, I define and explore the conceptual space of embodiment for information visualization. For visualizations, embodiment refers to the level of congruence between the visual elements of the visualization and their physical shape. This concept subsumes previously introduced concepts such as tangibility and physicality. For example, tangible computing aims to represent virtual objects through a physical form but the form is not necessarily congruent with the virtual object. A second problem is the scarcity of convincing applications of tangible user interfaces for infovis purposes. In information visualization, standard computer displays and input devices are still widespread and considered as most effective. Both of these provide however opportunities for embodiment: input devices can be specialized and adapted so that their physical shape reflects their functionality within the system; computer displays can be substituted by transformable shape changing displays or, eventually, by programmable matter which can take any physical shape imaginable. Research on such shape-changing interfaces has so far been technology-driven while the utility of such interfaces for information visualization remained unexploited. In this thesis, I suggest embodiment as a design principle for infovis purposes, I demonstrate and validate the efficiency and usability of both embodied visualization controls and embodied visualization displays through three controlled user experiments. I then present a conceptual interaction model and visual notation system that facilitates the description, comparison and criticism of various types of visualization systems and illustrate it through case studies of currently existing point solutions. Finally, to aid the creation of physical visualizations, I present a software tool that supports users in building their own visualizations. The tool is suitable for users new to both visualization and digital fabrication, and can help to increase users' awareness of and interest in data in their everyday live. In summary, this thesis contributes to the understanding of the value of emerging physical representations for information visualization.