Trends and Issues in the Use of Quantitative Color Schemes in Refereed Journals

This article reports on color usage in quantitative thematic mapping, drawing from an evaluation of maps published in eight geographical journals over the ten-year period from 2004 to 2013. During this period we found that color has become the preferred method to represent quantitative data sets, with the percentage of quantitative color maps relative to all quantitative maps rising from 18.4 percent in 2004 to 69.9 percent in 2013. We reviewed a sample of 440 maps from this period to assess the nature and appropriateness of their respective color schemes. We found the following frequencies of color scheme usage: spectral (30 percent), sequential (25.9 percent), diverging (25.7 percent), traffic (7.7 percent), and uncategorized (10.7 percent). Each scheme exhibited a distinct set of significant associations with particular map and data attributes, including subject matter, symbolization method, data polarity, and map size. Diverging and sequential schemes were the most effective, having strong associations with five key questions that we used to evaluate map effectiveness; for example, both schemes tended to be completely effective in terms of communicating spatial patterns and representing quantitative data values. Despite their popularity, spectral schemes were demonstrably unreliable and ineffective. Both spectral and traffic schemes were problematic for those with color vision deficiencies. Given the problems that we found with the use of various colors schemes, we make several suggestions for improving the design of maps appearing in refereed journals.