How can appropriate hue ranges be selected for sequential color schemes on choropleth maps? A quantitative evaluation using map-reading experiments

We propose map-reading experiments to quantitatively evaluate the selection of hue ranges for sequential color schemes on choropleth maps. In these experiments, 42 sequential color schemes with six base hues and seven hue ranges were employed as experimental color schemes, and a total of 414 college students were invited to complete identification, comparison, and ranking tasks. Experiments using both maps with synthetic data and real data were performed, each involving a web-based survey and an eye-tracking experiment. In the experiments using maps with synthetic data, the shapes of the map objects were relatively regular, and the attribute data were randomized. In contrast, the shapes were complex in the experiments that used maps with real data. Our findings show that widely used color schemes with a hue range of 0° yield poor performance in all tasks. Large hue ranges of 120–360° achieved good performance in the identification task but poor performance in the comparison and ranking tasks and yielded relatively low ratings. The hue range of 60° was favored by participants, who achieved excellent performance in the comparison and ranking tasks and acceptable performance in the identification task. Our findings suggest that a hue range of 60° is appropriate for designing sequential color schemes for choropleth maps.