How to Make Good Charts

What do you see?

What do you see?

It’s not just an illusion - it’s a photo

Why Graphics Matter

Graphics are a form of external cognition that allow us to think about the data rather than the chart

Good graphics take advantage of how the brain works

preattentive processing
perceptual grouping
awareness of visual limitations

Example

Spot the Difference

Preattentive perception

Occurs automatically (no effort)
Color, shape, angle
Combinations of preattentive features require attention
- Unless you double-encode
  (use different features for the same variable)

Using preattentive features reduces the amount of work your viewer has to expend to understand your chart

What do you see?

Gestalt Laws of Perception

The Gestalt laws are a set of rules for how we interpret ambiguity in the visual scene.

The law of Closure says that it’s easier to interpret things if you imagine them as a closed figure - it’s more likely that a closed figure is for instance obstructed, than that it is a set of more complex, less meaningful figures. This is sometimes also stated as the “law of good figure”

the law of Proximity says that things that are close together are likely part of the same unit. So you might interpret things as a dalmation instead of a series of blobs of black ink.

The law of continuation says that figures with edges that are smooth are more likely to be continuous than things with edges that are sharp angles.

the law of similarity says that things are likely to be viewed as part of a group if they look similar.

Then, the law of figure/ground helps explain why we see both the tree and the AL figure combination here - we have contextual information that helps us simplify the picture into two groups - the figure (the tree), and the background (the AL); thsi also helps us separate the AL from the white background behind it.

There are a few other gestalt laws, but these are the main ones.

Now, let’s talk about how these laws apply to charts! I swear, I didn’t forget that I am supposed to be talking about data visualization.

Gestalt Laws in Data Visualization

Proximity
Similarity

Gestalt Laws in Data Visualization

Good continuation

Which one is different?

Plot Annotations Matter!

Plot 12: 59.1%
Plot 5: 9.1%
Other plots: 31.7%

Plot 12: 9.7%
Plot 5: 29.0%
Plot 18: 32.3%
Other plots: 29.0%

Visual Limitations

Not all graphical representations are equally accurate
Optical illusions
Designing plots for disabilities

Accuracy of Graphical Judgements

Position along a common scale (most accurate)
- scatter plot
Position along nonaligned scale
- multiple scatter plots
Length
- bar chart
Angle, Slope
- pie chart
Area
- bubble chart
Volume, Density, Color saturation
- heatmap
Color hue (least accurate)

Optical Illusions

Designing for Accessibility

Write good alt-text and ensure it’s included in your online work
Low visual acuity:
- High contrast (bright/dark)
- large font size
- textures/patterns can be hard to make out
Colorblindness:
- Safest: design for a black-and-white photocopier
- Avoid rainbow gradients
- If you need a 2-color gradient, use blue/purple - white - orange (safe for most types of colorblindness)
Other options:
- ajrgodfrey/BrailleR - translate plots into text descriptions for screen readers
- sonify - represent data using sound
- gt - tables with metadata that is easy for screen readers

How to Make Good Charts

What do you see?

What do you see?

It’s not just an illusion - it’s a photo

Why Graphics Matter

Example

Spot the Difference

Spot the Difference

Preattentive perception

What do you see?

Gestalt Laws of Perception

Gestalt Laws in Data Visualization

Gestalt Laws in Data Visualization

Gestalt Laws in Data Visualization

Which one is different?

Which one is different?

Plot Annotations Matter!

Visual Limitations

Accuracy of Graphical Judgements

Optical Illusions

Designing for Accessibility

Questions?