Testing Digital Map Accessibility for Blind and Low-Vision Users

Smith-Kettlewell’s Brandon Biggs and colleagues built a systematic way to test whether a non-visual map conveys the same information as a visual one, and found that common text-based alternatives like data tables and turn-by-turn directions fall short.

Why digital maps are inaccessible to blind and low-vision users

Worldwide, at least 2.2 billion people have a vision impairment, according to the World Health Organization. For the blind and low-vision individuals among them, an everyday task most people never think about, pulling up a map to find a building, plan a route, or understand a neighborhood, is often impossible online.

Accessibility law is supposed to close that gap. Much of the world has adopted the Web Content Accessibility Guidelines (WCAG), which require that non-text content, like an image or a map, come with a text alternative serving the “equivalent purpose” — the version a screen reader actually reads aloud. But no one had defined what “equivalent purpose” actually means for something as information-dense as a map. Smith-Kettlewell engineer Brandon Biggs and his colleagues set out to pin it down, and to turn it into a test any map maker could apply.

The work grew out of a practical frustration. “There are currently so few digital maps that are accessible,” Biggs said. Rather than argue case by case about whether a given map “counts” as accessible, the team built a framework that measures it.

What makes a non-visual map accessible under WCAG

The result is the Map Equivalent-Purpose Framework, or MEP Framework. It breaks a map’s purpose into three parts, the generalized purpose, the spatial information it carries, and the spatial relationships between features, and then spells out 15 measurable criteria a non-visual map must meet to communicate the same content as its visual counterpart.

To put the framework to work, the team evaluated eight text-based map representations against visual map baselines, checking each against the 15 criteria. Three members of the team assessed the formats independently, then harmonized and integrated their scores into a single evaluation, so the judgment rested on more than one reviewer. The approach is deliberately holistic: a map substitute has to convey all of a visual map’s generalized spatial information and relationships, not just some convenient subset.

Which digital map formats are accessible to blind and screen reader users?

The formats that work are the ones that preserve spatial relationships, not just facts — what a blind user gets through a screen reader or audio has to carry the layout, not merely the labels. Legacy text methods, including data tables and turn-by-turn directions, failed the MEP Framework and fell short of basic digital accessibility standards, because they flatten a map into a list and lose how places relate to one another. Three approaches met the criteria: Audiom maps, an interactive non-visual map engine developed in the Coughlan Lab; Multi-user Domain (MUD) maps; and detailed audio descriptions.

The distinction matters because a table can tell you a park exists without ever telling you it sits between your home and the bus stop.

“A table communicates the numeric and text properties of a map, no geographic information when a map is used as an accessible text map alternative. Logically, one can look at the table and agree that it does not have the same information as the visual map, but the MEP Framework tells you exactly what is missing from the table. This is extremely helpful when having conversations with digital accessibility experts who have been recommending tables.”— Brandon Biggs, Engineer, Smith-Kettlewell Eye Research Institute

Why accessible digital maps matter for independence and civic life

Maps underpin more than sightseeing. They shape how people navigate cities, choose where to live, follow the news, and take part in civic life, and a growing number of professions assume everyone at the table can read one. When maps are inaccessible, blind and low-vision individuals are quietly shut out of all of it.

By clarifying what WCAG’s “equivalent purpose” requires and making it measurable, the MEP Framework gives developers and organizations a replicable, defensible standard for building maps that work, and a clear target to design toward instead of guessing. It also settles a question that had been left open: accessible digital maps are achievable now, and formats like Audiom already meet the bar. The payoff is direct. With a real standard to build to, blind and low-vision users gain full access to the maps that increasingly organize professional and civic life.