Fluid Interaction for Information Visualization Niklas Elmqvist * Andrew Vande Moere Hans-Christian Jetter Daniel Cernea Harald Reiterer T. J. Jankun-Kelly Abstract Despite typically receiving little emphasis in visualization research, interaction in visualization is the catalyst for the user’s dialogue with the data, and, ultimately, the user’s actual understanding and insight into this data. There are many possible reasons for this skewed balance between the visual and interactive aspects of a visualization. One reason is that interaction is an intangible concept that is difficult to design, quantify, and evaluate. Unlike for visual design, there are few examples that show visualization practitioners and researchers how to best design the interaction for a new visualization. In this paper, we attempt to address this issue by collecting examples of visualizations with “best-in-class” interaction and using them to extract practical design guidelines for future designers and researchers. We call this concept fluid interaction, and we propose a operational definition in terms of the direct manipulation and embodied interaction paradigms, the psychological concept of “flow”, and Norman’s gulfs of execution and evaluation. Keywords: fluidity, flow, embodiment, design, information visualization, human-computer interaction. 1 Introduction Not all information visualization (InfoVis) tools are created equal. As all users of such tools know, while we can expect any competent tool to be able to represent abstract data in graphical form, there is a certain class of InfoVis tools that take this a step further through engaging, compelling, and even absorbing user experiences that turn the analytical sensemaking [45] process into a pleasurable task. However, the academic portion of the InfoVis field in general puts little emphasis on design, aesthetic, and user experience aspects of information visualization tools, and so far there has been virtually no effort towards characterizing this class of InfoVis tool in the research community. In contrast, much of information visualization in the real world is directly concerned with creating compelling—even playful—and beautiful tools that are capable of capturing the attention of general users on the Internet and in public spaces such as museums, exhibition halls, and corporate lobbies. In this article, we try to remedy this state of affairs by proposing a unifying concept for both researchers and practitioners that captures this class of InfoVis exemplars in a single definition: fluid interaction. Fluidity in information visualization is an elusive and intangible concept characterized by smooth, seamless, and powerful interaction; responsive, interactive and rapidly-updated graphics; and careful, conscientious, and comprehensive user experiences. Our hypothesis is that an InfoVis tool that exhibits this fluidity in all aspects will transform the sensemaking process into an efficient, illuminating, and even enjoyable experience because it helps the user stay in the flow [13] of the work process. However, creating a fluid design is far from trivial, mainly because of this intangibility and elusiveness. To better illustrate our definition of fluid interaction for information visualization, we collect and describe a subset of these exemplar InfoVis tools from the scientific community, including BabyNameVoyager [58], Facet-Streams [30], and Scat- ter/GraphDice [9, 17]. Unlike most existing research articles in information visualization, we also collect exemplars from outside the scientific community, such as from the design, aesthetics, and infographics communities. These “real-world” exemplars include mæve [4, 36, 39], We Feel Fine [22], and the interactive holographics from the film Iron Man 2 [12]. Using these exemplars as a starting point, we derive tips, guidelines, and principles for how to achieve fluidity in InfoVis in terms of both interaction and visual representations. We hope that these snippets of practical experience, elevated almost to the level of being design idioms and patterns [21], will help developers of InfoVis tools—academics and practitioners alike—to build better, more rewarding, more captivating, and ultimately more efficient information visualization tools that will propel our field to make an even bigger impact in both our own scientific community as well as the real world. In the rest of this paper, we first survey the state of the art in fluid interaction, design, and user experience for information visualization (Section 2). We then attempt to define the concept of fluid interaction through a detailed list of properties that we think characterize fluid InfoVis tools (Section 3). These properties are all exhibited in the context of our InfoVis exemplars, that * School of Electrical & Computer Engineering, Purdue University, 465 Northwestern Ave, West Lafayette, IN 47907, USA, E-mail: elm@purdue.edu. 1