Context is the surrounding information that lets an audience understand a visualization: relevant events, circumstances, explanations, text, images, symbols, and sources. It turns an extracted pattern into knowledge by answering the question “Why does this situation happen?” rather than leaving readers with a chart alone. section 1.4.2 section 7.1
Build context after identifying the main point. Use it as the story’s background to set the scene and raise interest; then use a call to action to invite next steps. An exploratory chart may reveal an insight, but an explanatory visualization supplies the background and motivation needed to communicate it to a particular audience. section 5.2.1 section 5.1.2
Choose context that explains the insight and suits the audience:
- Add factual explanations of conditions, events, or comparisons that account for a pattern. section 1.4.2 section 2.3.2
- Use commentary before the insight to establish background; use annotations to attach an explanation directly to the chart. section 7.1 section 7.3
- Reinforce a message with visual cues such as highlights, images, or a baseline when they clarify why selected values matter. section 4.5.2
- Place context before the main point—at the top, left, or within the chart. A top subtitle can provide an overview or credit a data source. section 8.6 section 8.6.1
Explain participation, not just percentages
A pet-event chart shows far more cats than dogs. The number of advertised websites supplies useful context: 150 cat sites versus 28 dog sites. Calculating participants per advertised website gives rates of 7.59 for cats and 4.64 for dogs, helping explain the difference. A title, header, and pet images then make that context easier to read. section 1.4.2
Annotate a tourism trend
Portugal’s tourist arrivals rose by more than 200% over 25 years. A chart annotation attributes this increase to the introduction of low-cost flights, while a small passenger-traffic line chart provides supporting context. In Altair, create annotation text with mark_text(), build the supporting trend with mark_line(), and combine the charts. section 2.3.2
Textual context must be calibrated to readers. Adults may not need an explanation of money, while children may need denominations and the monetary system explained. For generated commentaries or annotations, specify a ChatGPT role, audience, topic, and text type; iterate by adjusting these elements until the wording fits. section 7.1 section 7.3
Table 1.3 Data related to pets involved in the event, with a focus on the participants’ rates
|
Pet
|
Number of Participants
|
Percentage
|
Number of Advertised Websites
|
Participants-to-website rate (# of participants/#
of websites)
|
|---|---|---|---|---|
|
Cat
|
1138
|
88.56
|
150
|
7.59
|
|
Dog
|
130
|
10.12
|
28
|
4.64
|
Compare raw participation counts, advertised-site counts, and participant-to-website rates to see how a derived measure provides explanatory context. section 1.4.2
