A system's visual displays can be considered its face. With well-designed displays, the interplay among a system's functions, parts, processes, data structures, and agents becomes less abstract and more like the familiar countenance of a partner. Both displays and faces can be described formally as collections of metric and categorical relationships among features. Some properties of both displays and faces acquire special psychological status, as when a collection of display elements signals "all normal" in a safety-critical system, or when a collection of facial features conveys happiness. Displays and faces can be responsive or impassive, expressive or inscrutable, trustworthy or unreliable. Unlike faces, however, displays are totally ours to design.In this chapter, we discuss problems that designers confront in the development of displays, and we look at data-driven principles of human perception, cognition, and action that can help solve them. We focus on visuospatial analog displays, which use perceptual dimensions such as extent and brightness to represent the values of system variables. We draw from and expand upon design principles offered by Gillan, Wickens, Hollands, and Carswell (1998); Hegarty (2011); Kosslyn (2006); Robertson, Czerwinski, Fisher, and Lee (2009); Wickens, Lee, Liu, and Gordon-Becker (2003); as well as others. Readers wanting to know more about the empirical foundations of individual principles are directed to Ware (2013) and Wickens, Hollands, Banbury, and Parasuraman (2013).
DESIGN ELEMENTS AND DESIGN PROBLEMSDesign elements used to create analog displays have three main functions. First, display dimensions are the properties of display objects that designers vary to represent data values. Thus, bar charts represent data by varying the height (display dimension) of bars (display objects). Facilitators, such as labels, legends, and axes, are a second functional design element. They are added to displays to help users locate, identify, and compare display dimensions. Finally, embellishments are intended to enhance visual interest or attractiveness, or to reinforce the display's general theme.Display formats are combinations of graphical objects, dimensions, and facilitators that have been standardized within a domain, such as scatterplots, box plots, and Pareto charts in statistical analysis or high-low-close charts in finance. In this chapter, we consider a variety of formats, but we single out one format-face displays-to illustrate many design dilemmas. If displays can sometimes seem like faces, then it is not surprising that designers have sometimes used faces as displays (e.g., Chernoff, 1973). In Figure 25.1, face displays are part of a fictional learning management system (LMS) dashboard, intended to help instructors monitor the progress of students. The features of six faces are used to represent outcomes for six students. For example, the width of the mouth is used to represent classroom participation. Although Figure 25.1 demonstrates