92526 Chap.10 Choosing Graphs for Fast Perception
Choosing Graphs for Fast Perception
The Week 3 material asks what makes a graph good, beyond picking a template. Visualisations are fast: a reader takes in a trend from a picture far more quickly than from a table, which the slides show with a footballer's weekly training-intensity trace, binned and smoothed to reveal different features.
The chapter sets out the ranking of visual encodings shown in Week 3, from position on a common scale at the top down through length, angle, area, colour saturation and shape, and uses it to explain why bars usually beat pies.
It then matches charts to purposes: comparison, correlation, distribution, part-to-whole and data over time, each with an alternative suited to different data.
Finally it covers the Gestalt principles of proximity, similarity, common region and common fate, the limits of working memory and change blindness.
What this chapter covers
- 01
Why visualisations speed up understanding
- 02
Ranking of visual encodings
- 03
Comparison and correlation charts
- 04
Distribution, part-to-whole and time charts
- 05
Proximity and similarity in subplots
- 06
Common region and common fate
- 07
Working memory and change blindness
Worked example · free
Rank three designs for comparing squad sprint times
- 1Design B is first: bars encode the times by position and length on a common scale, the easiest encodings to compare.
- 1Design A is second: a pie relies on angle and area, below position on the ranking, and a part-to-whole picture does not suit averages that are not shares of a total.
- 1Design C is last: colour saturation sits near the bottom of the ranking, so small differences between squads become very hard to judge.
Key terms
- Proximity principle
- The Gestalt tendency to read objects placed close together as a group.
- Similarity principle
- The Gestalt tendency to group items that share colour, shape or another visual feature.
- Common region
- The Gestalt tendency to treat elements enclosed in one shared area as belonging together.
- Heatmap
- A chart that shows magnitude as colour across two dimensions, useful when many points overlap.
- Change blindness
- Difficulty noticing differences between two similar scenes, a risk when comparing separate static plots.
Choosing Graphs for Fast Perception FAQ
How do you choose the right type of chart?
The Week 3 page says the choice depends on the type of data and on how you want the reader to perceive it, meaning where, how and how quickly their attention should land. Charts are grouped by purpose: comparison, correlation, distribution, part-to-whole and data over time, with alternatives within each purpose.
Why are bar charts usually easier to read than pie charts?
The ranking of visual encodings shown in Week 3 puts position on a common scale at the top, because people compare it most accurately; length, angle and slope share a lower rank and area sits below them. Bars place values by position on a common scale; pies rely on angle and area, so the same comparison is harder to make from a pie.
When is a heatmap better than a scatterplot?
A scatterplot shows every raw observation, outliers and linear trends between two variables. When there are so many points that they overlap, a heatmap aggregates them into counts for regions of the plot and shows those counts as colour, which makes dense data readable again.
What do proximity and similarity mean for graph design?
Proximity says objects placed close together appear to form a group, so put the comparisons that matter most next to each other in subplots. Similarity says items with the same appearance are grouped, which is why colouring bars or points by a category helps readers see which belong together.
Why limit the number of categories in a chart?
Working memory is limited, and the Week 3 slide notes that seven categories already decrease readability and increase comprehension time. Fewer categories, direct labels and consistent scales across subplots keep a figure fast to read, which is the reason for visualising data in the first place.
Exam move
Learn the encoding ranking as an ordered list and practise using it to critique real charts, from club reports to sport broadcasts: name the encoding each chart uses and whether a higher one was available. Build a one-page table of the five chart purposes with the main chart and its alternative for each, and test yourself by matching short coaching questions to a chart.
Then redesign one cluttered figure using proximity and similarity, cutting categories and labelling directly. This turns the Week 3 principles into decisions you can explain in a sentence, which is the habit the Week 3 activities ask for.
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