Evaluation of persuasiveness of selected map designs for presenting dominance of phenomena on thematic maps

Various editorial decisions made during the cartographic design process may lead to different interpretations of the same phenomena, potentially emphasizing one phenomenon at the expense of another. Such decisions occur at different stages of map development, including the selection of enumeration units, a form of data representation (map type), and map graphics, including color scales.

This article presents the results of a user study examining the impact of selected map design choices – specifically: a level of spatial unit aggregation, a type of color scale, and a form of data presentation (a qualitative area map, a choropleth map, a cartogram, graduated symbols with choropleth colors) – on the accuracy of perceiving the dominance of a phenomenon shown on thematic maps. The study employed thematic maps visualizing two socially relevant topics: ethnonational diversity and presidential election results, each displaying two categories. The survey, conducted using the CAWI (Computer-Assisted Web Interviewing) method, involved 151 participants. Respondents were asked to identify which of the two categories was dominant on a given map. Response accuracy (identification of the actual dominant phenomenon), the perceived difficulty of the tasks, and the perceived magnitude of dominance were measured. Participants were also asked to describe the spatial distribution of the dominant phenomenon and indicate a map design preferred by them.

Based on the collected responses, the analysis revealed statistically significant differences in metrics depending on the map designs tested. The tested map designs, therefore, vary in their degree of persuasiveness in portraying dominance. The article concludes by identifying the techniques that more or less effectively distort the information conveyed by thematic maps.