Assessing the Effectiveness of Temporal Legends in Environmental Visualization

The increasing prevalence of interactive visualization applications for the representation of spatiotemporal environmental data has created a need for research into the cartographic design of these dynamic applications. The understanding of temporal animations requires that users not only perceive the spatial information presented, but also, just as importantly, be able to locate that information in time and understand changes across time. Temporal legends can support these needs by prompting appropriate schemata or mental models for interpreting the temporal component of dynamic maps and by providing a method through which users can control what they see. Little empirical research has been directed toward discovering the relative advantages and disadvantages of the various different legend styles that have been designed to indicate the temporal location of an animation. This paper reports on an assessment of the relative effectiveness of three types of temporal legends to communicate information and facilitate visual thinking. These three types have been selected from a much larger set of legend styles currently in use for spatiotemporal data presentation and exploration. Our general hypothesis is that the effectiveness of a temporal legend depends to a significant extent on both the task (what questions are being answered) and the application (what phenomenon is being investigated) for which it is implemented. The results of this assessment will be important for the future design of well-reasoned cartographic animations intended to facilitate study of any type of spatiotemporal process.