Published by the IEEE Computer Society 0272-1716/07/$20.00 © 2007 IEEE IEEE Computer Graphics and Applications 15 Guest Editors’ Introduction Visualization has been the cornerstone of scien- tific progress throughout history. Much of mod- ern physics is a result of the superior abstract visualization abilities of a few brilliant men. New- ton visualized the effect of gravitational force fields in three dimensional space acting on the center of mass. And Einstein visualized the geo- metric effects of objects in relative and uniform accelerated motion, with the speed of light a constant, time part of space, and acceleration indistinguishable from gravity. Virtually all com- prehension in science, technology, and even art calls on our ability to visualize. In fact, the ability to visualize is almost synonymous with under- standing. We have all used the expression “I see” to mean “I understand.” 1 T he need to make sense of complex, con- flicting, and dynamic information has provided the impetus for new tools and technologies that combine the strengths of visualization with pow- erful underlying algorithms and innovative interaction techniques; tools that make up the emerging field of visual analytics. 2 Visual analytics is the formation of abstract visual metaphors in combination with a human information discourse (usually some form of interac- tion) that enables detection of the expected and dis- covery of the unexpected within massive, dynamically changing information spaces. It is an outgrowth of the fields of scientific and information visualization but includes technologies from many other fields, includ- ing knowledge management, statistical analysis, cog- nitive science, decision science, and others. This marriage of computation, visual representation, and interactive thinking supports intensive analysis. The goal is not only to permit users to detect expected events, such as might be predicted by models, but also to help users discover the unexpected—the surprising anomalies, changes, patterns, and relationships that are then examined and assessed to develop new insight. The “Visualization Time Line” sidebar gives a brief summary of some of the key developments associated with visualization that have led to the current situation. In addition to introducing the articles in this special issue, this column sets out some of the key issues and challenges associated with discovering the unexpected. Interfaces and interaction In visual analytics, the key purpose of visualizations and interaction techniques is to help the user gain insight into complex data and situations where models alone are insufficient and human analytic skills must be employed. Visualizations must not only support the rep- resentation of critical data features but also provide suf- ficient contextual cues to help the user rapidly interpret what he or she is seeing. Interaction techniques strive to enable users to go beyond data exploration to achieve a dialogue with their information space to detect trends and anomalies, evaluate hypotheses, and uncover unex- pected connections. Computer scientists wish to develop effective interfaces to computers that facilitate communication and interac- tion between the human and the information in the machine. In the past, the importance of interface design has not always been fully recognized, or it may have been even ignored completely. Today, good design is increas- ingly recognized as being a key requirement for a user interface to be usable, flexible, and successful. With the current proliferation of computing devices, including mobile phones, PDAs, and other handheld devices, design is even more important in order to enable the user to man- age the complexity that this introduces. With the intelli- gence in these devices, they can communicate with each other and reduce the cognitive load they place on the user. However, if information is filtered before it is pre- sented to the user, how do we ensure that it is filtered appropriately and that key information that subsequent- ly turns out to be important is not omitted or deleted? Studies have focused on the ways that users interact with different kinds of devices. For example, the human perception of information on a mobile phone is different from that on a wall-size display. We need to be aware of these differences and the opportunities and constraints that they present both for the display of information and also the user’s interaction with it. Kris Cook Pacific Northwest National Laboratory Rae Earnshaw University of Bradford, UK John Stasko Georgia Institute of Technology Discovering the Unexpected