Conceiving and Reasoning Visualization Design Options - Data Visualization: A Successful Design Process - page 108

• Visual annotation : Annotation goes beyond just written explanations
and we should consider how to use chart or graphic devices to help draw
out important insights visually. Simple options include features such as
gridlines, axes labels, and tick marks. In Chapter 3 , Demonstrating Editorial
Focus and Learning About Your Data , we saw an example of effective
visual annotation. Here, reference lines and background shading is used
effectively to help the reader achieve distinction between different tiers
of interpretation, as you explore the relationship between what countries
spend on education and the military.
Image from "In Numbers: Education Around the World" ( http://visualdata.dw.de/specials/
bildung/en/index.html ), created by Gregor Aisch for Deutsche Welle
• Legends and keys : Always explain the use of color schemes or the varying
size of shapes in terms of their categorical or quantitative representation.
• Units : You should include details of the units of values being displayed to
ensure you don't create ambiguities and potential misinterpretation. As with
many of these annotated features, this is an obvious requirement, something
we've had drilled into us since our school days, but you'd be surprised how
often they can be left out.