Choosing a chart
Five intentions (compare, trend, composition, distribution, relationship) and the chart for each, how precisely visual encodings can be read, and four traps: truncated axis, dual axis, 3D effect, too many categories.
- 24 cards
- 6 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- Concepts
- Questions
- Sort and link
- The numbers
- Scenarios
- Understand
A few cards from the deck
Data visualisation: what is it?
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A representation of data through shapes (position, length, colour) so the eye can quickly spot a comparison, a trend or an exception.
The choice starts from the question asked of the data: the same table of figures calls for different charts depending on whether you compare, track or look for a link.
Which chart shows the share of each of the three channels (shop, website, phone) in the year's revenue?
- A pie chart with three slices
- A histogram with three bins, one per channel
- A line joining the three channels
- A scatter plot of channel against revenue
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A pie chart with three slices
Showing each element's share of a whole is a composition: a pie fits when the slices are few (so does a 100% stacked bar). A histogram splits a continuous measure into bins, not categories.
To follow a trend over time, choose a …; to see how values are distributed (for example customers' ages), a ….
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To follow a trend over time, choose a line chart; to see how values are distributed (for example customers' ages), a histogram.
The line joins points ordered in time and shows the slope. The histogram groups values into classes and shows the shape of their spread.
Chart type: what is it?
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A standard form of representation, such as bars, line, scatter plot, histogram or pie, suited to an intention of reading.
Bars: compare. Line: follow over time. Scatter plot: relate two measures. Histogram: see a distribution. Pie: a composition, with few slices.