Increasing Accessibility for Map Readers with Acquired and Inherited Color Vision Deficiencies: A Re-Coloring Algorithm for Maps

Approximately 8% of the male population suffer from an inherited form of color vision deficiency (CVD). Age, diabetes, macular degeneration, cataracts and glaucoma result in eye defects including an acquired form of CVD. Inherited CVD is marked by a difficulty in discerning red from green, while acquired CVD is marked by a difficulty in discerning blue from green. A recent review of the cartographic literature revealed a deficit in studies on accessible maps for readers with the acquired form of CVD. In addition, research on accessible maps for readers with the inherited form of CVD was restricted to the design or pre-publication stage. An approach is needed to render maps already in circulation accessible to an audience with CVD. The purpose of this research is to improve the accessibility of maps post-publication. Image re-coloring is a method of altering an image's color composition in such a way as to make it accessible to a color vision deficient audience. An innovative algorithm is presented that produces a re-colored map that can be perceived by individuals with red-green (inherited) CVD, blue-green CVD (acquired) and normal color vision alike. The algorithm was tested on a control group of participants with normal color vision and a case group of participants with impaired color vision through a series of matching, content and personal preference questions about six pairs of maps. Each map pair represented one of the following color schemes: balance, diverging, qualitative area, qualitative dot, sequential polychrome, and two variable. Each map pair is composed of two renditions: a map using a color palette that is potentially confusing to viewers with impaired color vision (original rendition) and a map where the original color palette has been re-colored by the algorithm (re-colored rendition). According to the results of a Wilcoxon signed-rank test, the performance of the case group improved when using the re-colored renditions compared to when using the original renditions while the performance of the control group was the same for both renditions. A Mann-Whitney rank sum test revealed that while the scores of the case group were lower than the control group when using the original renditions, they were the same when using the re-colored renditions. A binomial test revealed that subjects in the case group displayed a preference towards all the re-colored renditions while subjects in the control group displayed a preference to two of the six original renditions.