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
Continuous data axes
For continuous data axes centrally align labels over tick marks.
Example of how to format continuous data axes
Categorical data axes
For categorical data axes labels should be aligned between tick marks.
Example of how to format categorical data axes
Using more ticks than labels
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.
Example of how to format ticks and labels
Economic inactivity rate for people aged 16 to 64 years
UK, January 1980 to October 2014
Legends or keys
Using a legend or key
A legend or key should not 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.
Example of how to use a legend or key
Example of how not to use a legend or key
Order and orientation
The order and orientation of the legend or key should be the same as the data.
Example of how to order a legend or key
Example of how not to order a legend or key
Long category names
Using long category names
Use a horizontal bar chart rather than a vertical bar chart if your data have long category names.
Example of how to format a bar chart with long category names
Example of how not to format a bar chart with long category names
Subcategories
Labelling the 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.
Example of how to label categories and subcategories
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.
Examples of how to write chart titles and subtitles
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.
Example of how to use annotations to draw attention to secondary messages
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.
Example of how to write a descriptive title for visual content
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.
Example of how to write a title for an exploratory tool
Chart labels
Horizontal text
Chart text must be horizontal. If the labels will not fit into the required space, transpose the chart or convert the units.
Example of how to format text in a chart
Unemployed adults aged 16 to 64 years by region
England, 1993
Example of how not to format text in a chart
Unemployed adults aged 16 to 64 years by region
England, 1993
Right alignment of y-axis values
Your y-axis values should always be right-aligned to make them as easy as possible for users to read.
Example of how to align y-axis values
Pets by nation
UK, 2012
Labelling values in a chart
Use of data value labels
Bar charts should not need data value labels. If you need data value labels, create a chart−table combination.
Example of a chart−table combination
If you cannot create a chart−table combination, make sure the data value labels are placed at the base of each bar and right-aligned.
Example of how to format data value labels in a bar chart
Things to avoid
Avoid putting the values at the end of each bar, as this makes it difficult for users to follow and compare the values.
Example of how not to format data value labels
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.
Annotations do not display on mobile devices. Essential information should be included in the main text or footnotes and not in annotations. This is because most users access the ONS website using a mobile phone or tablet.
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 or quality section 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 refer to or direct users to footnotes in another 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.
Source
A source for each chart must be provided in the following format:
[PUBLICATION OR SOURCE OF DATA] from the [ORGANISATION]
We use words rather than punctuation or symbols to tell users which sources have provided data that are used in the visual. This is more accessible for all users.
Annual Survey of Hours and Earnings from the Office for National Statistics
Pay As You Earn Real Time Information from HM Revenue and Customs
Local Land Charges Research from the Land Registry
More than one source
If the chart is compiled using more than one source, then list them all by dividing them with commas. However, if the list becomes very long then just provide the three most important sources.
Labour Force Survey from the Office for National Statistics, Value Added Tax (VAT) returns from HM Revenue and Customs, and the School Census from the Department for Education
Multiple sources from the same organisation
If you have multiple sources from the same organisation, you can include the organisation name only once.
Value Added Tax (VAT) returns and Pay As You Earn Real Time Information from HM Revenue and Customs, and the Labour Force Survey from the Office for National Statistics
We are constantly improving based on research and best practice. Any significant changes to our guidance are available on the Updates page.