The Influence of Uncertain Map Features on Risk Beliefs and Perceived Ambiguity for Maps of Modeled Cancer Risk from Air Pollution

Abstract

Maps are often used to convey information generated by models, for example, modeled cancer risk from air pollution. The concrete nature of images, such as maps, may convey more certainty than warranted for modeled information. Three map features were selected to communicate the uncertainty of modeled cancer risk: (a) map contours appeared in or out of focus, (b) one or three colors were used, and (c) a verbal-relative or numeric risk expression was used in the legend. Study aims were to assess how these features influenced risk beliefs and the ambiguity of risk beliefs at four assigned map locations that varied by risk level. We applied an integrated conceptual framework to conduct this full factorial experiment with 32 maps that varied by the three dichotomous features and four risk levels; 826 university students participated. Data was analyzed using structural equation modeling. Unfocused contours and the verbal-relative risk expression generated more ambiguity than their counterparts. Focused contours generated stronger risk beliefs for higher risk levels and weaker beliefs for lower risk levels. Number of colors had minimal influence. The magnitude of risk level, conveyed using incrementally darker shading, had a substantial dose-response influence on the strength of risk beliefs. Personal characteristics of prior beliefs and numeracy also had substantial influences. Bottom-up and top-down information processing suggest why iconic visual features of incremental shading and contour focus had the strongest visual influences on risk beliefs and ambiguity. Variations in contour focus and risk expression show promise for fostering appropriate levels of ambiguity.

Testing Map Features Designed to Convey the Uncertainty of Cancer Risk

“…Previously unanalyzed data on adequacy judgments, collected as part of the Severtson and Myers (2013) study, were used to address study aims. The full factorial 2 × 2 × 2 × 4 study (resulting in 32 study maps) was designed to test how three dichotomous map features across four cancer risk levels influenced dependent variables.…”

“…This decreases the need to consult the legend in order to understand the symbol’s meaning, which facilitates comprehension (Robinson & Petchenik, 1976). Features proposed to foster bottom-up comprehension of magnitude (Cleveland & McGill, 1985) iconically resemble magnitude to some extent, such as incremental shading or incremental length to convey incremental magnitude (Severtson & Myers, 2013). Cartographers recommend using incrementally darker color shades on maps to represent incremental magnitudes of a phenomenon (Brewer, 2006).…”

“…Given that focused and unfocused contours have some resemblance to certainty and uncertainty, contour focus is proposed as an iconic method for representing uncertainty on maps (Severtson & Myers, 2013). …”

“…Previous findings showed that several map features led to more perceived ambiguity (Severtson & Myers, 2013). However, the analysis did not examine participants’ subjective evaluations of the information as recommended by risk communication researchers (Bostrom et al, 2008; Lipkus, 2007).…”

More Than Meets the Eye: Volcanic Hazard Map Design and Visual Communication

“…The results suggest that visualisation of hazard data on a map can influence the information that people take away. Modified from Thompson et al (2015) wildfire (e.g., Cheong et al 2016), hurricane (e.g., Broad et al 2007;Sherman-Morris et al 2015), flooding (e.g., Strathie et al 2015), sea level rise (e.g., Retchless 2014), and health (e.g., Severtson and Myers 2013). For example, researchers have found that visual design of wildfire hazard maps can influence people's interest and engagement with the hazard information and also how they use it to make decisions about evacuation (Cao et al 2016;Cheong et al 2016).…”