Effective Data Visualisation

A good chart makes the answer obvious. A poor one hides it, or worse, misleads. The difference usually comes down to a handful of design choices.

Here are ten practical tips for creating visualisations and dashboards that are clear, honest and easy to act on.

Why it matters

People understand a well-designed chart in seconds that would take minutes to work out from a table. Trends, outliers and comparisons stand out, people remember what they saw, and when everyone looks at the same picture, the discussion moves from "what's happening?" to "what should we do?"

1. Know your audience

Executives need the headline and the exceptions. Analysts need detail and the ability to explore. Design for the people who'll use the visual, and the decision they need to make. Microsoft's report design guidance makes the same point: talk to some of the people who'll use the report before placing visuals, and show them an early draft for feedback.

2. Choose the right chart

Line charts for trends, bar charts for comparisons, maps for geography and scatter plots for relationships. If you need a legend to explain a pie chart with eight slices, use a bar chart instead.

3. Simplify and focus

Remove anything that doesn't add meaning, such as 3D effects, heavy borders and unnecessary gridlines. Limit each dashboard page to the few visuals that answer its main question, and don't use two visuals to show the same thing. In Power BI, too many visuals on a page also slows the report down.

4. Use colour with purpose

Use a neutral palette and reserve strong colour to highlight what matters, such as a target missed. Keep colours, terms and layouts consistent across reports, so people learn them once, and check colours work for people with colour vision deficiency (see "Design for everyone" below).

5. Provide context

A number on its own means little. Show it against a target, last year or a benchmark, and use clear titles, labels and units. Avoid acronyms and jargon in titles: "Current year sales (AUD)" is clearer than "CY Totals".

6. Add interactivity where it helps

Filters, drill-down and tooltips let people answer their own follow-up questions. Keep interactions simple and predictable, and don't hide key information behind an interaction or a tooltip. People who don't use a mouse, and screen readers, can't always reach it.

7. Tell a story

Arrange visuals in a logical order, from overview to detail, and use titles that state the insight, such as "Unplanned downtime doubled in February".

8. Design for every screen

Many people check dashboards on phones and tablets. Create mobile layouts and test them.

9. Keep it honest and current

Start bar chart axes at zero, avoid distorted scales and show uncertainty where it exists. Automate refreshes, show when the data was last updated and build every report on a shared, governed data model so the numbers agree. Trust is hard to win back once a chart has misled someone.

10. Test and improve

Watch people use your dashboard, ask what they're looking for and refine it. Usage data shows which reports are valuable and which can be retired.

Design for everyone

An accessible dashboard is a clearer dashboard for everyone. These checks come from the Web Content Accessibility Guidelines (WCAG) and Microsoft's accessibility guidance for Power BI:

• Text contrast: titles, labels and data labels need a contrast ratio of at least 4.5:1 against their background (3:1 for large text). That's WCAG 2.2 success criterion 1.4.3, level AA.
• Chart contrast: the parts of a graphic needed to understand it, such as each line in a line chart, need at least 3:1 contrast against adjacent colours (WCAG 1.4.11).
• Never rely on colour alone: add markers with different shapes to line and scatter charts, or use text and icons alongside colour.
• Avoid hard-to-tell-apart pairs in the same chart or page, such as green and red, green and brown, blue and purple, and light green and yellow. Fewer colours, or a monochrome palette, helps.
• Alt text: describe the insight of every visual that conveys meaning (Power BI allows up to 250 characters, and can make it dynamic with a measure).
• Keyboard order: set the tab order to match how people read the page, and remove decorative shapes and images from it.

Power BI also gives report users a screen-reader-friendly table of any visual's data (Alt+Shift+F11), and a high-contrast view. A quick low-vision test is to turn your screen brightness right down and see what still stands out.

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