What is an annotation?

Annotation:

“a note by way of explanation or comment added to a text or diagram.”

Synonyms: notation, comment, footnote; commentary, explanation.

Sometimes referred to as data labels or captions, annotations are often added to charts to add an extra layer of useful information for the reader. Think of it like using a highlighter on a block of written text. We can purposefully guide our readers to view certain aspects of the data that are important.

Why are they so useful?

Annotations can help:

add a narrative to guide the audience and offer commentary for your graphic

add clarity to remove ambiguity and confusion

highlight or validate a particular point to emphasise key messages in your data

encourage the audience to compare different data points or highlight a particular range

call out at a specific point at a particular time in an animation

by replacing a legend – using explanations directly on the chart can help the audience understand your symbology correctly

We all love stories

As storytelling becomes more prevalent in map-making, adding text is probably our best way to introduce narrative. As cartographers, we can look to data journalism for inspiration. If you look at data visualisations from The Financial Times or New York Times, you will see how they masterfully include text into their graphics. If the explanations form an integral part of the graphic, then it becomes self-encapsulating and is useful on its own. This improves sharing and embedding.

Some tips for your map annotations

Place annotations on the chart as close as possible to the data points of interest.

Subtle changes can greatly decrease or improve readability – take the time to refine your design.

Remove your legend – if your map doesn’t contain a large number of individual symbols, then the use of direct labelling may negate the necessity for a legend.

Show people your map to see how they interpret it. If they’re confused, you can explain it more clearly using annotation.

Consider where you want the annotations to sit within the visual hierarchy. Do you want them to be read first or be there as a supporting feature? If you make them stand out too much then there is a danger that they could detract from your data.

Use leader lines or arrows to connect your notation to the data.

If you want your annotations to appear as a different ‘layer’ of your graphic, you can always try using a hand-sketched style like this great example by Reuben Fischer-Baum of The Washington Post.

See more hints and tips from the GeoDataViz team.