The impact of point symbol similarity on visual search on maps

Abstract

The study presented in this paper investigates the impact of the similarity level of cartographic point symbols on visual search performance. Specifically, we explore the application of an algorithm for quantitatively assessing symbols’ shape similarity, and apply the results of such automated analysis in a simple target search task on a map with distractors of varying similarity levels. Our primary hypothesis posits that the more similar the target symbol and distractors, the more challenging the visual search becomes in terms of search efficiency and eye metric performance. In a controlled laboratory experiment utilizing eye-tracking device, 33 participants were recruited, and 60 map stimuli were tested with each participant. The results confirmed the hypothesis assumptions. However, symbols based on a round shape were consistently the easiest to find at every similarity level. Eye movement analysis revealed differences in absolute pupil size between male and female participants, possibly associated with cognitive load, although without affecting search time performance. Interestingly, scan-path speed decreased with an increasing level of similarity between the target symbol and distractors. The practical implication of this study lies in the potential development of tools to assist map designers in selecting symbols with low similarity, thereby ensuring improved map readability.