This presentation is about a lecture I gave within the "Green Lab" course of the Computer Science master, Software Engineering and Green IT track of the Vrije Universiteit Amsterdam: http://masters.vu.nl/en/programmes/computer-science-software-engineering-green-it/index.aspx http://www.procaccianti.me

1. 1 Het begint met een idee
Data Visualization
Giuseppe Procaccianti

2. Vrije Universiteit Amsterdam
2 Giuseppe Procaccianti / S2 group / The Green Lab
Quick Recap: Experimental Process
Experiment
scoping
Experiment
planning
Idea
Experiment
operation
Analysis &
interpretation
Presentation &
package

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3 Giuseppe Procaccianti / S2 group / The Green Lab
What is Data Visualization?
«The use of computer-supported, interactive,
visual representations of abstract data to
amplify cognition».
Readings in Information Visualization: Using Vision to Think. S.K.Card, J.D.Mackinlay, and B.Shneiderman,
Academic Press, 1999

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4 Giuseppe Procaccianti / S2 group / The Green Lab
Examples of amplified cognition

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5 Giuseppe Procaccianti / S2 group / The Green Lab
More examples of amplified cognition
WTF Visualizations: http://viz.wtf/

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6 Giuseppe Procaccianti / S2 group / The Green Lab
Data visualization: science or art?

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7 Giuseppe Procaccianti / S2 group / The Green Lab
Data visualization theory
Quantitative communication

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8 Giuseppe Procaccianti / S2 group / The Green Lab
Quantitative communication
Quantitative values (measures)
Categorical information (groups)

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9 Giuseppe Procaccianti / S2 group / The Green Lab
Quantitative communication: example
Categorical information (name)
Categorical information (group)
Quantitative values

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10 Giuseppe Procaccianti / S2 group / The Green Lab
Quantitative communication: example
Both
Categorical
Quantitative

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11 Giuseppe Procaccianti / S2 group / The Green Lab
Tables vs. graphs
Tables
● Easy look-up of values
(comparisons)
● Precise values
● Different units of
measure are possible
Graphs
● Overall "shape" of data
(trends)
● Reveal relationships
between multiple
variables

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12 Giuseppe Procaccianti / S2 group / The Green Lab
Data visualization theory
Graphical Integrity

13. Vrije Universiteit Amsterdam
13 Giuseppe Procaccianti / S2 group / The Green Lab
Graphical integrity [1]
● Data visualization must tell the truth
[1] Edward R. Tufte, 1983. The Visual Display of Quantitative Information. Graphics Press.
● Avoid misleading information and chartjunk

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14 Giuseppe Procaccianti / S2 group / The Green Lab
Graphical integrity: principles
● Proportionality
● Utility
● Clarity

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15 Giuseppe Procaccianti / S2 group / The Green Lab
Proportionality: Lie Factor
● Ideal LF = 1
○ if LF > 1 you are overstating an effect
○ if LF < 1 you are understating an effect

16. Vrije Universiteit Amsterdam
16 Giuseppe Procaccianti / S2 group / The Green Lab
Proportionality: Lie Factor
Data Visualization
5.3/0.6 = 8.83
27.5/18 = 1.53
LF=5.77

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17 Giuseppe Procaccianti / S2 group / The Green Lab
Utility: data ink
● Ideal Data-Ink ratio != 1
○ a balance must be found between readability and utility

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18 Giuseppe Procaccianti / S2 group / The Green Lab
Utility: data ink

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19 Giuseppe Procaccianti / S2 group / The Green Lab
Utility: data ink

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20 Giuseppe Procaccianti / S2 group / The Green Lab
Clarity

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21 Giuseppe Procaccianti / S2 group / The Green Lab
Clarity

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22 Giuseppe Procaccianti / S2 group / The Green Lab
Data visualization theory
Information Encoding

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23 Giuseppe Procaccianti / S2 group / The Green Lab
How to encode information in a graph
● Quantitative information
○ Points: relative position
○ Lines: relative position, slope, length
○ Bars: length (height)
○ (2D) shapes: area

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24 Giuseppe Procaccianti / S2 group / The Green Lab
Points

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25 Giuseppe Procaccianti / S2 group / The Green Lab
Lines

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26 Giuseppe Procaccianti / S2 group / The Green Lab
Lines

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27 Giuseppe Procaccianti / S2 group / The Green Lab
Bars
Width plays
no role!
Zero-based
scale (LF)

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Columns

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29 Giuseppe Procaccianti / S2 group / The Green Lab
2D shapes (the infamous pie chart)
Always put
percentages!

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30 Giuseppe Procaccianti / S2 group / The Green Lab
2D shapes (the infamous pie chart)

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31 Giuseppe Procaccianti / S2 group / The Green Lab
How to encode information in a graph
● Categorical information
○ Position (along an axis)
○ Color
○ Shape
○ Fill
○ Linestyle

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32 Giuseppe Procaccianti / S2 group / The Green Lab
Position, color

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33 Giuseppe Procaccianti / S2 group / The Green Lab
Shape

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34 Giuseppe Procaccianti / S2 group / The Green Lab
Next lab session: ggplot tutorial
● R advanced graphics package
● https://cran.r-project.org/web/packages/ggplot2/index.html
● REMINDER: Wednesday 9am!!

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35 Giuseppe Procaccianti / S2 group / The Green Lab
References and further readings
● Graph design principles, M. Torchiano (slides) on BB
● Edward R. Tufte, 1983. The Visual Display of Quantitative
Information. Graphics Press.
● Manuel Lima: A visual history of human knowledge

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36 Giuseppe Procaccianti / S2 group / The Green Lab
Thank you!
g.procaccianti@vu.nl
i.malavolta@vu.nl