Geoscience is a colorful research field. Rock formations’ hues provide clues about their makeup. Colors preserved in fossils can shed light on how ancient organisms looked.
And expansive rainbows of colors are used to highlight key information on maps of everything from the atmosphere to the ocean floor. But such maps are not always accessible for scientists with color vision deficiency (CVD, or “color blindness”)—a condition that researchers estimate affects more than 300 million people globally.
Inclusive color maps can help ensure information is easily interpreted by scientists, and using them in public weather communications could even help save lives.
In a study published in the Bulletin of the American Meteorological Society, researchers—two of whom have color vision deficiency themselves—demonstrated how radar maps can be made accessible to people with deuteranopia and protanopia, two types of color vision deficiency that make it difficult or impossible to distinguish red and green.
“The goal was to create a more CVD-friendly color map based on discussions with individuals who are having a hard time reading these color maps,” said Zachary Sherman, a software engineer at Argonne National Laboratory in Lemont, Ill., and an author of the study.
New Use of Color and Light
The team focused on making maps that are more perceptually uniform in terms of both color and lightness. In a perceptually uniform color scheme, changes in color and changes in data values are weighted equally to the typical human eye, without sudden breaks. That means that in a gradient of shades from blue to green, for example, the amount of difference between any two adjacent shades looks about the same. In contrast, having an uneven variance between colors can make some differences on a map appear larger or smaller than they are, particularly to those with color vision deficiency. The researchers applied the same concept to evenly weighting differences in lightness.
They also used a principle called perceptual order, in which lightness increases linearly, to avoid creating the perception of gradients the map is not meant to depict. These changes are important because many people with CVD have trouble distinguishing green and red shades of equal lightness.
Completely perceptually uniform maps would be missing key information, however. So the maps still include “meaningful breaks in colors,” but “only when we truly needed [them]” to depict information such as where convection is and isn’t present in storms, Sherman said.
The team created accessible versions of maps for four different kinds of storms, including a pyrocumulonimbus storm, in which heat from Earth’s surface leads to the formation of thunderclouds, and a wintertime midlatitude cyclone.
“We wanted to test different storms because the breaks in convection and nonconvection, different storms at different latitudes, and [more] tend to require different parameters,” Sherman said.
Community Dialogue
From its onset, the mapping project has been community-centric. It started when coauthor Cameron Homeyer, a meteorologist at the University of Oklahoma, posted about the topic on Twitter/X.
Because “the Python [computer programming] community as a whole has been pushing more toward accessible color maps,” the discussion quickly migrated to GitHub, Sherman said. Users became part of an informal focus group that provided feedback on the new color maps.
Next, the team presented their maps at conferences and asked attendees, “If you’re willing to say, do you have CVD? Does this help you?”
“I was quite shocked by how many members of the community actually had [color vision deficiency].”
“I was quite shocked by how many members of the community actually had CVD,” Sherman said. For example, at one conference in the Netherlands, one of the cochairs with color vision deficiency said that the storm features were much easier to pick out on the new maps, Sherman noted. After a different conference talk, faculty told him that some of the new color maps were “making a huge difference” for students who hadn’t been able to use legacy color maps.
Simon Jowitt, an economic geologist at the University of Nevada Reno, has color vision deficiency affecting his ability to distinguish reds and greens and, to a lesser extent, blues and yellows. When looking at maps, he said, it can be difficult for him to distinguish what colors represent the minimum and maximum values of what the map is portraying.
“One has to look at the contouring of the color to determine which is maximum and minimum, [compared to] people with full color vision, who could presumably tell at a glance. This slows down interpretation and makes one cautious on how data are viewed,” Jowitt wrote in an email to Eos.
He added that the maps created by Sherman and colleagues were “easier to interpret” and had a more intuitive color scheme than legacy maps. However, he said the minimum and maximum values still appeared relatively similar. “Perhaps cutting off the spectrum a little earlier at one end may help discriminating between max and min values,” he said.
Maps for the Seeing Public
“In weather maps, there is a real need to check the imagery and color schemes for their inclusivity.”
Besides helping researchers and students, more inclusive color maps could help protect the public from dangerous storms. When legacy maps are used in weather television or internet broadcasts and on weather applications, many people with color vision deficiency don’t see them as they’re intended to be seen. For instance, radar images that show two sources of winds whirling together, such as in a hurricane, often use red and green. This can make it difficult for those with color vision deficiency to see the danger of the whirlpool shape, Sherman said.
“In the weather maps and much more, I think there is a real need to check the imagery and color schemes we use for their inclusivity for the large number of people who have some form of color vision deficiency,” Jowitt said.
Sherman said that he and his colleagues will continue to work with the community to refine their maps. This includes working to create maps that will be accessible to people with full color vision deficiency, which “is much more difficult,” he said.
—Rachel Crowell (@writesRCrowell), Science Writer
