Line styles

Use solid lines, dotted lines and dashed lines to differentiate between time series. This also means lines look more distinct when printed in black and white or if a user is colour-blind.

Axis labels and tick marks

For continuous data axes centrally align labels over tick marks.

For categorical data axes labels should be aligned between tick marks.

You can use more tick marks than labels; ticks indicate the scale or level of detail of the data.

Label the final tick if there are more ticks than labels and there is space to do so.

Economic inactivity rate for people aged 16 to 64
UK, January 1980 to October 2014

Legends or keys

A legend or key shouldn’t be used, instead label the data directly. If a legend or key is necessary, place it on the chart as close as possible to the data.

The order and orientation of the legend or key should be the same as the data.

Long category names

Use a horizontal bar chart rather than a vertical bar chart if your data has long category names.

Subcategories

If the subcategories are not the same in all of the main categories, label the main categories and subcategories directly on the y-axis.

Chart titles

Label charts as a figure and number them in order. Figures should have a main title and a statistical subtitle. Titles and subtitles should be concise and in sentence case.

Main title

The main title should be descriptive, and tell the trend of the data or highlight the main story. Try to limit the number of words to no more than 10. This should make the description easier to read and avoid the text wrapping onto several lines, especially on mobile devices.

If you need to add context or detail to the chart, use annotations or support with your analysis.

Statistical subtitle

The statistical subtitle should be as short as possible and must include the:

  • statistical measure
  • geographic coverage
  • time period

You do not need to include these elements in the subtitle if they are already in the main heading.

Writing chart titles to support your analysis

When writing your chart title and analysis:

  • use chart titles to complement or build on, but not repeat section headings
  • add further context and explanation of the chart’s message in your main text
  • do not try and summarise everything the chart says in the title, but prioritise the main message

Take care not to use language in a title that you would not use in your analysis. Exaggerated language such as “greatest rise ever” may be more eye-catching, but use sparingly as it may appear sensationalist or could potentially be misinterpreted.

It can be useful to draw attention to a record level being recorded in the most recent data, but if a new record continues to be set every month, using the same title will lose its impact. Use sparingly and find another message to concentrate on instead.

Your title can refer to a shorter period than shown on the chart. You can highlight an important short-term trend and give broader context by using a longer timeframe in your chart and analysis.

If your chart has more than one message

If a chart has more than one narrative, choose the one that will be most relevant to users for the main title. Use annotations to draw attention to secondary messages, but do not try and explain every nuance in the chart when your analysis can provide more detail.

Titles for other visual elements

Other types of visual content can communicate information. If you are using a flow chart or a map, the same titling principles apply. Use a descriptive title to tell the user what the story behind the image is, and use a statistical subtitle if appropriate.

Sometimes a graphic may genuinely be one you wish your user to explore – there is no immediate story or message on display. For example, some of the interactive graphics coming from the Data Visualisation team may be in this space. In these rare cases, it is acceptable to use a title that encourages the reader to explore the graphic.

Chart labels

Chart text must be horizontal. If the labels won’t fit into the required space, transpose the chart or convert the units.

Unemployed adults age 16 to 64 by region
England, 1993

Unemployed adults age 16 to 64 by region
England, 1993

Right align y-axis values.

Pets by nation
UK, 2012

Labelling values in a chart

Bar charts shouldn’t need data value labels. If you need data value labels, create a chart−table combination.

If you can’t create a chart−table combination, make sure the data value labels are placed at the base of each bar and right-aligned.

Annotation and footnotes

Chart annotations can be very useful to highlight key messages in your data. They must be concise and relevant. Place annotations on the chart as close as possible to the data points of interest.

Avoid chart footnotes where possible. If extra information is needed:

  • annotate the chart
  • include the information in the statistical commentary accompanying the chart
  • add a footnote to the chart title

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