Start with the question the data answers
State the question or decision before drawing. Are you comparing a trend, distribution or a few exact values? Choose a form that reveals the relationship, and use a table when every number matters more than the overall shape.
Show scope, units, period and source near the figure. A percentage without its denominator or an unexpectedly truncated axis can mislead. The measurement guide
- Question and unit explicit.
- Source and period visible.
- Chart chosen for the relationship.
Explain the content outside the image
Give the visual a short alternative identifying its subject. For a complex chart, add a long description visible to everyone or a table of values. Explain trends, gaps and exceptions needed to understand the conclusion.
W3C advice on complex images distinguishes short identification from detailed information. A long string of values in an alt attribute is difficult to hear; structured HTML may serve readers better.
- Subject named in the alternative.
- Values and trends available as text.
- Long description structured where needed.
Test colours, scales and screens
Do not rely on colour alone to distinguish series. Add labels, patterns or markers and check contrast. On a phone, verify axes and values without demanding constant horizontal zoom.
A table needs headers associated with cells even when the layout narrows. If a mobile chart is simplified, do not remove an essential series. The accessibility guide
- Series distinct without colour.
- Axes readable on mobile.
- Table headers understandable.
Verify numbers over time
Name the source, collection date, method and owner. When data changes, check title, conclusion, table and translations. A chart image may remain in an article after the underlying data is corrected.
Review any downloads too: reusable format, column names and absence of data that should not be public. A clear figure cannot redeem a faulty calculation; have values reviewed before release.
- Source and calculation reviewed.
- Copies and translations updated.
- Downloads checked.