Effectiveness of animated choropleth and proportional symbol cartograms for epidemiological dashboards

Epidemiological maps on COVID-19 dashboards were critical to disseminating information during the pandemic, but dashboard creators faced difficulties avoiding common misinterpretation pitfalls that result from varying population density. Furthermore, most dashboards did not include animated maps despite their intuitive visual analogy to the temporal unfolding of events. This study explores the effectiveness of population cartograms as a basis for animated maps showing the progression of a pandemic. The ability to recall locations of peak case rates per population was compared for subjects receiving animated maps and cartograms overlaid with proportional symbols and choropleth colors representing case counts and rates per population, respectively. Results confirm that map readers often confuse case counts with rates on standard proportional symbol maps and fail to notice small, densely populated enumeration units on standard choropleth maps. Population cartograms reduced these common visual biases for both map forms, but map readers were unable to track rates per population on proportional symbol cartograms even with prior instruction. Although animations of standard choropleth maps and colored proportional symbol cartograms were most preferred by subjects, choropleth cartograms are recommended for consideration by dashboard creators as they effectively communicate case rate trends while avoiding visual biases associated with other map types.