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Displaying Quantitative Information

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Displaying Quantitative Information

An exploration of Edward R. Tufte’s

The Visual Display of Quantitative Information

Jeffrey Nichols

Programming Usable Interfaces

May 2, 2003

Napolean’s invasion of Russia, as drawn by Charles Joseph Minard (1781-1870)

The price of wheat compared to labour wages, William Playfair (1759-1823)

French train schedule, as drawn by E.J. Marey (1830-1904)

Map of the northern galactic hemisphere

(1.3 million galaxies shown)

Tufte presents some principles of data graphics

- Above all else, show the data.
- Maximize the data-ink ratio
- Erase non-data-ink
- Erase redundant data-ink
- Revise and edit

- Ink that changes as the data changes

- Non-redundant ink!

data-ink

Data-ink ratio =

Total ink used to print graphic

=Proportion of a graphic’s ink devoted to the non-redundant display of data-information.

=1.0 – proportion of graphic that can be erased without the loss of information

What is the data-ink ratio of this graphic?

< 0.05 !!!

- What is the data-ink ratio of this graphic?

< 0.001

Tufte presents some principles of data graphics

- Above all else, show the data.
- Maximize the data-ink ratio
- Within reason
- Every bit of ink on a graphic requires a reason

- Erase non-data-ink
- Erase redundant data-ink
- Revise and edit

Tufte presents some principles of data graphics

- Above all else, show the data.
- Maximize the data-ink ratio
- Erase non-data-ink
- Erase redundant data-ink
- Revise and edit

11

5

2

1

0

18

7

Histogram of Midterm Results

# of Students

A-

B+

A

B

B-

C

Scoring Buckets

11

5

2

1

0

18

7

Histogram of Midterm Results

# of Students

A-

B+

A

B

B-

C

Scoring Buckets

18

11

5

2

1

0

7

Histogram of Midterm Results

What’s the data-ink ratio?

# of Students

A-

B+

A

B

B-

C

Scoring Buckets

Tufte presents some principles of data graphics

- Above all else, show the data.
- Maximize the data-ink ratio
- Erase non-data-ink
- Erase redundant data-ink
- Revise and edit

Box Plots

Maximum

75%

Median

25%

Minimum

Box Plots

Maximum

75%

Median

25%

Minimum

Bar Graphs

Modified Graph

Original Graph

Scatter Plots

Modified Graph

Original Graph

Another Scatter Plot Variant

- Show data variation, not design variation
- Avoid using ink for non-data items
- Avoid redundancy
- Clear and detailed labeling should be used to defeat graphical distortion
- Revise and Edit

Questions?

Thanks for a great class!

Reminder:

Final Exam on Friday, May 9th at 8:30am in this room

- Graphical Integrity
- The representation of numbers, as physically measured on the surface of the graphic itself, should be directly proportional to the numerical quantities represented.
- Clear, detailed, and thorough labeling should be used to defeat graphical distortion and ambiguity. Write out explanations of the data on the graphic itself. Label important events in the data.
- Show data variation, not design variation.
- In time-series displays of money, deflated and standardized units of monetary measurement are nearly always better than nominal units.
- The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data.
- Graphics must not quote the data out of context.

- Theory of Data Graphics
- Above all else, show the data.
- Maximize the data-ink ratio
- Erase non-data-ink
- Erase redundant data-ink
- Revise and edit

- Other comments
- Graphical elegance is often found in simplicity of design and complexity of data
- Data graphics are paragraphs about data and should be treated as such