During dashboard week, we explored designing viz for visually impaired people. One very useful tool that can be utilised for this are screen readers.
The typical Windows Narrator can be enabled by holding Ctrl + Windows and pressing the Enter button. However, there is also the Google Chrome Screen Reader which has few additional functions including reading tooltips.
There are a few limitations to basic screen readers:
1) No reading of Tooltips (except Chrome Screen Reader)
2) The Marks in your Viz
3) Axis labels and titles
4) Headers
When using screen readers, there are a few points to be aware of:
1) Know your audience!
People who use screen readers are as diverse as the people who don't use them. This means that you don't have to always simplify the figures to meet a more lay audience.
2) Make use of as much of the data as possible
As you lose the ability to view figures from the marks, illustrate as much of your data including calculated fields where possible. People using screen readers will still want to know these insights.
3) Provide a set of instructions in the beginning
Each screen recorder may have different functionalities and navigations. Clearly mention this in a text box at the beginning of the viz. You may want to highlight this box so that people who do not use screen readers may know what these instructions are.
4) Add a description of objects that can't be screen read.
Maps are a good example of this as they may hold important information. When highlighting over a map without a description, the screen reader may not indicate what the object is and what its showing. By simply stating "The following map displays the profit ratio for each state" will suffice.