Keywords: data visualization, annotation, communication, education
Visualization should be easy, it's just pictures of data! The truth is much more complicated, of course. The readers and users of charts (and even more so, interactive visualizations) need to know and understand many concepts to get the full benefit of a chart. There is the basic ability to read a chart: what do the shapes mean? While most people can read a bar chart, scatterplots, treemaps and other more exotic charts are less familiar and many people simply don't know how to read them. Then there is the data: what is this about? What is being measured, what are the axes, what does up or down mean, etc. And even once all that is known, do we know if a pattern we see is actually meaningful or just a coincidence or artifact?
In data journalism, the concept of the annotation layer is commonly invoked to help with this: annotations help the reader understand a chart by explaining the data, the visualization, interesting shapes and patterns, etc. Because it is done "in-situ" directly on the chart, rather than as a separate introduction or explanation, it makes for a much more direct, useful, and perhaps memorable way of helping the reader understand what is being shown.
In this talk, I will show some examples (which go back at least to the late 1800s), review some relevant literature on visualization literacy, annotations, memorability, etc., and show some new ideas for how annotations can be used in more modern and adaptive ways to help people better see and understand their data.