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# Chart Design

## CAPP 30239

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## Today

- What general **principles of visual design** are relevant to our work?
- What are the **common types of charts** and how do we use them?
- When and how do we break the rules?

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## Edward Tufte

### The Visual Display of Quantitative Information

![](tufte.png)

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## Key Ideas

- Graphical Integrity: Above all else, show the data.
- Maximize the data-ink ratio.
- Minimize chart-junk.
- Aim for high chart density, consider *small multiples*.
- Revision & Editing are essential.

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## Tufte's Principles for **Graphical Integrity**
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1. The representation of numbers, as physically measured on the surface of the graphic itself, should be directly **proportional** to the numerical quantities represented.

![](liefactor.jpg)

Mileage increase: 53%
Graph length increase: 783%
"Lie Factor": 14.8x

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2. Clear, detailed and thorough **labeling** should be used to defeat graphical distortion and ambiguity.

![bg left](spinal.webp)

How many children get a spinal injury every year? (out of 74,000,000 children in US)

<!-- .0000003% -->

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3. Write out explanation of the data on the graphic itself. **Label important events** in the data.

![](labeled.png)

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4. Show **data variation, not design variation**.

Deflated & standardized units of money are almost almost superior to nominal units.

The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data. (roughly 1:1 channel mapping)

Exception: It is OK/common to pair color & shape, or for print color & texture to address issues that color presents.

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## Data-Ink Ratio

- **Data-ink**: Ink (pixels) used to show data.
- Data-ink ratio: data-ink / total-ink

![](francetrains.jpg)

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![](eec.gif)

![bg right width:600px](sizecycle.gif)

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## Optimizing Data Density

Number of entries in DataFrame / Area of Graphic.

Classic example of high data density is the sparkline, which can fit on a line of text.

![](sparkline.png)

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![bg left height:700px](age-junk.png)

## Chart Junk

Anything that isn't relevant to understanding the data.

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![](chartjunk-bullet.webp)
via junkcharts.typepad.com

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## Common Chart Types

### Bar Charts & Histograms

### Line & Area Charts

### Sparklines

### Strip Plot & Heatmap

### Pie / Donut / Radial Charts

### Ranked Line Chart

### Scatterplots

### Small Multiples / Faceting

### Distributions

### Map Basics

### Altair Gallery Miscellania

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## When & How to Break the Rules

### 2 Examples: Hex / Grid maps ... Word Clouds
### Narrative-supporting graphics
### When it's OK to use 3D

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## Acknowledgements & References

Thanks to Alex Hale, Andrew McNutt, and Jessica Hullman for sharing their materials.

- https://www2.cs.uh.edu/~ceick/NO/COSC3337-DV2.pdf