By its nature, data visualisation is only accessible to sighted people: blind persons do not enjoy the benefits of data visualisation. While we are already having a hard time determining what the optimal way is to present numbers to sighted people, making data and numbers understandable to blind people is especially challenging, and requires converting numbers and the patterns in data into information that can be perceived by other senses than sight.
But next to people who lack sight completely, there is a much bigger group of people who suffer from some kind of partial loss of sight. These conditions include daltonism (different kinds of colour blindness), myopia, farsightedness and glaucoma. People suffering from these conditions can still have access to the advantages of data visualisation, but they require data visualisations to have an optimal design and digital and analog tools to gain access.
However, in order to make sense of data visualisations, sight alone is not enough. People need to understand what rules were used to translate numbers into the visual elements presented to them, how to decode the data in a chart, and finally be able to take away the main message of a visualisation. This requires cognitive capacities, familiarity with charts and numeracy from your audience. Ignoring this will lead to a mismatch between the interface (= the data visualisation) and the people using it to get access to the data.
Making data visualisation accessible to people with visual impairments and making visualisations understandable for as many people as possible, is the main topic of this training. To do so, we can apply the POUR principles introduced on the web accessibility page. But because the POUR principles were not specifically developed with data and data visualisation in mind, 3 other principles are added to POUR: Compromising, Assistive and Flexible.
The so called POUR-CAF principles were developed by the designers of the Chartability framework, a set of tests to ensure the accessibility of visualisations and interfaces. The Chartability framework is properly introduced in Intro to Chartability.