Table of contents

  1. Line styles
  2. Axis labels and tick marks
  3. Legends or keys
  4. Long category names
  5. Subcategories
  6. Chart titles
  7. Chart labels
  8. Labelling values in a chart
  9. Annotation and footnotes

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Annotation and footnotes

Using annotations

Chart annotations can be useful to tell your data’s story. They must be concise and immediately relevant, for example, to highlight important trends or dates on the chart that help the user understand the data. 

Place annotations on the chart as close as possible to the data points of interest. Avoid using too many annotations as this is likely to overwhelm users and reduce their effectiveness. We recommend only including three to four annotations per chart. 

The chart builder tool we use to create charts on the ONS website has a limit on the length and number of annotations that can be included and where they can be placed. They should be limited to around 50 characters (10 to 12 words) and be no more than one sentence. 

Using footnotes

Footnotes should be limited to important information needed for users to understand and interpret a chart or table. They should only be used to refer to the data specifically used in that chart or table. If a footnote refers to data used in general throughout the bulletin or article, this should be worked into the surrounding commentary instead. 

Avoid using too many footnotes as they can make the page long and interrupt the flow of the analysis, which is especially off putting for users on mobile devices.  

Footnotes should: 

  • be clear and concise 
  • spell out any acronyms used in the chart or table 
  • not include information that belongs in the main text 
  • avoid repetition of survey names – this should be included in the source 

Footnotes must be presented in context with the chart they relate to. They should not be placed in a separate section where they require the user to scroll up and down the page.  This is to ensure that if the chart is reused or if a user views only one chart, they get the information they need in order to understand the data. 

Example of how to use annotations and footnotes in a chart

Number of divorces1
England and Wales, 1910 to 2011

Footnotes (include at end of accompanying copy text)
1 Divorce figures include both decree absolutes and decrees of nullity

We are constantly improving based on research and best practice. Any significant changes to our guidance are available on the Updates page.