A study on the aptitude of color hue, value, and transparency for geographic relevance encoding in mobile maps

Depicting the right amount of information on mobile maps is still challenging. With this research we investigate which of the three visual variables hue, value, and transparency optimally directs visual attention to the correct encoding of the geographic relevance of on small displays? We hypothesize that transparency is best suited to let users see symbols in the correct order of high to low relevance and that they intuitively understand this encoding of symbols for value and transparency, but not for hue. In a user study with 27 participants, we tested the suitability of the three visual variables for mobile maps with eye tracking. Results for a perceptual viewing task where no further knowledge or a task was provided, showed no significant differences between the three visual variables for time to first fixation and scanning the symbols in the correct order of relevance. A second search task for the most relevant restaurant, results showed that only transparency seems to reliably encode geographic relevance. "Darker is more" is only partially understood and the traffic light metaphor is unsuitable for encoding ordered geographic relevance on mobile maps. These results are in line with other work and offer guidelines for mobile map design.