Data Science · Beginner level

Beginner level · Module 4: Visualisation and Data Storytelling · Lesson 1 of 3

Choosing the Right Chart

Match chart types to what you want to show: comparison, change over time, distribution or relationship.

In this lesson you will

  • Choose a chart type for each kind of message
  • Recognise misleading chart designs

Key concepts

comparison: bar charttrend: line chartdistribution: histogramrelationship: scatter plot

The lesson

Pick the chart from the message: compare categories with bar charts (sorted, starting at zero), show change over time with line charts, show distributions with histograms or box plots and show relationships with scatter plots.

Pie charts work only for a few parts of one whole; bar charts are almost always easier to read.

Charts mislead when axes are truncated to exaggerate differences, when areas or 3-D effects distort sizes or when important context such as sample size is missing.

Step by step

  1. Match ten messages to chart types.
  2. Redraw a pie chart as a sorted bar chart.
  3. Fix a bar chart with a truncated axis.
  4. Add missing context to a chart.
Troubleshooting tree

Which chart should I use?

Choose a chart from what you want the reader to see.

Do you want to show change over time?
  • Yes
    Use a line chart with time on the horizontal axis. Use a few lines at most and label them directly.
  • No
    Do you want to compare amounts across categories (districts, schools, sources)?
    • Yes
      Use a bar chart, sorted from largest to smallest, with the axis starting at zero. Highlight the category you are discussing.
    • No
      Do you want to show how values are spread out?
      • Yes
        Use a histogram for one group, or box plots to compare spreads across groups.
      • No
        Do you want to show the relationship between two numeric variables?
        • Yes
          Use a scatter plot, perhaps with a trend line; remind readers that a relationship is not proof of cause.
        • No
          Consider whether a table or a single, clearly stated number communicates the message better than any chart.

Notes

Whatever you choose: a title that states the finding, labelled axes with units, and a source note with the date and sample size.

Practice activity

Choose and sketch the three charts for the water brief and justify each choice.

Expected result: Three appropriate chart choices with clear reasons.

Check your understanding

  1. Which chart shows change over time best?

    Show answer

    A line chart.

  2. Why should bar charts start at zero?

    Show answer

    Bar length represents the value; a truncated axis exaggerates differences.

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