Graphs, charts and other methods of visualizing data can help people understand complicated information at a glance. However, they’re only effective for those with full vision. According to the National Federation of the Blind, 7.6 million people in the U.S. have a vision disability.
By making sure any data visualizations you use on NIU websites are accessible, you enable clear communication with this portion of our potential audience. You also help ensure our content meets legal requirements regarding accessibility. Start by making sure the chart/graph is labelled correctly, then check out these additional ways to improve its accessibility.
Color
When preparing a data visualization for use online, be careful about your color choices. WCAG accessibility guidelines require graphics to have at least a 3:1 contrast ratio with their background. Use the WebAim contrast checker to gauge accessibility.
In order to make your graphic accessible to people with color blindness, don’t use color as the sole indicator of meaning. For example, instead of using using different colored lines in a line graph, use a variety of line formats (solid, dots, dashes, etc.).
Text Descriptions
According to the Web Content Accessibility Guidelines (WCAG), images on websites, including data visualizations, must be accompanied by alternative (alt) text. The alt text for your chart or graph should describe the image, taking care to accurately impart the meaning it conveys. For example, instead of saying “Chart showing a breakdown of favorite pizza toppings,” you could say, “Chart showing that pepperoni is by far the most favorite pizza topping, followed by sausage, with olives and pineapple preferred by a few people each.”
You can also use the alt text to direct users to a longer text description that you work into the page content. To build on our previous example, you could add the following at the end: “For a more detailed explanation, read the Results section.”
By including a longer text description on the page, you’re not only making the information more accessible to those with visual disabilities, but also for those who prefer to process information verbally instead of visually.
Resources
