Now You See itTheory of Data Visualisation

Vinu CT

17 March 2015

What We Will Discuss

Visualisation Excellence/Integrity Theory of Data Visualisation

What We Will Not Discuss

Perception and Visualisation (Eye/Brain System) Specific programs to create graphics

Excluded: Sales & Emotion

Source: http://www.engadget.com/2008/01/15/live-from-macworld-2008-steve-jobs-keynote/

Graphical Excellence

“Excellence in statistical graphics consists of complex ideas communicated with clarity,

precision, and efficiency“

- Edward Tufte The Visual Display of Quantitative Information

Anscombe's QuartetI

II

III

IV

X

Y

X

Y

X

Y

X

Y

10

8.04

10

9.14

10

7.46

8

6.58

8

6.95

8

8.14

8

6.77

8

5.76

13

7.58

13

8.74

13

12.74

8

7.71

9

8.81

9

8.77

9

7.11

8

8.84

11

8.33

11

9.26

11

7.81

8

8.47

14

9.96

14

8.1

14

8.84

8

7.04

6

7.24

6

6.13

6

6.08

8

5.25

4

4.26

4

3.1

4

5.39

19

12.5

12

10.84

12

9.13

12

8.15

8

5.56

7

4.82

7

7.26

7

6.42

8

7.91

5

5.68

5

4.74

5

5.73

8

6.89

I II III IV

X Y X Y X Y X Y

10 8.04 10 9.14 10 7.46 8 6.58

8 6.95 8 8.14 8 6.77 8 5.76

13 7.58 13 8.74 13 12.74 8 7.71

9 8.81 9 8.77 9 7.11 8 8.84

11 8.33 11 9.26 11 7.81 8 8.47

14 9.96 14 8.1 14 8.84 8 7.04

6 7.24 6 6.13 6 6.08 8 5.25

4 4.26 4 3.1 4 5.39 19 12.5

12 10.84 12 9.13 12 8.15 8 5.56

7 4.82 7 7.26 7 6.42 8 7.91

5 5.68 5 4.74 5 5.73 8 6.89

Mean X 9

Y 7.5

Variance X 10

Y 3.75

Correlation (X,Y)

0.82

Equation of Reg. Line: Y = 3 + 0.5 X

The 1854 London Cholera Epidemic

Source: http://www.datavis.ca/gallery/historical.php

A silly theory means a silly graphic

Source: Tufte (www.wearethepractitioners.com/library/the-practitioner/2014/07/10/big-data-and-predictive-analytics)

Why Learn to Effectively Graph?

Visual representations not only make the patterns, trends, and exceptions in numbers visible and understandable, they also extend the capacity of memory, making available in front of our eyes what we couldn't otherwise hold all at once in our minds. In simple terms information visualization helps us think.

– Stephen Few

Graphical Integrity

A graphic does not distort if the visual representation of the data is consistent with the numerical representation

Lie FactorLie factor = size of effect shown in graphic / size of effect in data

Lie factor = 2.8

“The shrinking family doctor in California”, Los Angeles Times, p. 3, August 5, 1979

Theory of Data Visualisation

Data-Ink and Graphical Redesign Chartjunk

Data Ink

“Above all else show the data“ - Tufte

“A large share of ink on a graphic should present data-information, the ink changing as the data change. Data-ink is the non-erasable core of a graphic, the non-redundant ink arranged in response to variation in the numbers represented.”

High Data-Ink RatioLow Data-Ink Ratio

Erase redundant data-ink, within reasonSource: https://viscomvibz.wordpress.com/2012/02/26/the-visual-display-of-quantitative-information/

Data-Ink and Graphical Redesign

Data-ink Example

Click here

Chartjunk

Three widespread types of chartjunk:

Unintentional optical art The dreaded grid The self-promoting graphical duck

“The interior decoration of graphics generates a lot of ink that does not tell the viewer anything new. The purpose of decoration varies — to make the graphic appear more scientific and precise, to enliven the display, to give the designer an opportunity to exercise artistic skills. Regardless of its cause, it is all non-data-ink or redundant data-ink, and it is often chartjunk.”

Unintentional optical art

Why we don't use pattern fills?

Unintentional optical art - 2

Source:Journal of Economic Perspectives—Volume 28, Number 1—Winter 2014—Pages 209–234

Chartjunk

Graphing Quiz

What is the best way to display percentages (parts of a whole)?

What are all the problems with this graph?

Source: https://trinkerrstuff.wordpress.com/

Improved Version

Source: https://trinkerrstuff.wordpress.com/

What is the problem with this graph?

Source: https://trinkerrstuff.wordpress.com/

An Economist’s Guide to Visualizing DataJournal of Economic Perspectives—Volume 28, Number 1—Winter 2014—Pages 209–234

Show the data Reduce the clutter Integrate the text and the graph

Reference

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Next Sessions

Ggplot2: Data Visualisation in R Best Practices in Data Visualisation Perception and Visualisation

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