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Data Visualization

Chapter 1. Fundamentals of Graphical Practice

Iñaki Úcar

Department of Statistics | uc3m-Santander Big Data Institute

Master in Computational Social Science

Licensed under Creative Commons Attribution CC BY 4.0 Last generated: 2023-09-27

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Introduction to DataViz

The What, the Why and the How

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What is a Graph?

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What is a Graph?

"Visual representation of information to help people make sense of complex phenomena through data"

—Enrico Bertini

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Acclaimed Historic Examples

  • Joseph Priestley, 1765: first timeline chart as visual aid for his lectures

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Acclaimed Historic Examples

  • William Playfair, 1786: first bar chart

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Acclaimed Historic Examples

  • William Playfair, 1786: first line (timeseries) chart

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Acclaimed Historic Examples

  • William Playfair, 1789: first pie chart (sadly)

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Acclaimed Historic Examples

  • Florence Nightingale, 1858: polar area diagram that convinced the British Government to improve army hygiene

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Acclaimed Historic Examples

  • John Snow, 1854: map of cholera cases that helped identify the source

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Acclaimed Historic Examples

  • Charles Joseph Minard, 1869: first flow chart depicting Napoleon's 1812 Russian campaing

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Why Graphs?

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Why Graphs?

Convert data that our working memory cannot retain into direct visual stimuli that do not require "reading"

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Why Graphs?

Convert data that our working memory cannot retain into direct visual stimuli that do not require "reading"

  • We have a poor working memory (~ 7 elements)...
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Why Graphs?

Convert data that our working memory cannot retain into direct visual stimuli that do not require "reading"

  • We have a poor working memory (~ 7 elements)...
  • but our eyes have superpowers!
    • ~ 30% of our brain is dedicated to visual processing
    • We can process ~ 100 Mbps
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Why Graphs?

Visual reasoning is way faster and more reliable than mental reasoning

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Example: Find the Highest Number
345
33.4
627.8654
1.0057632
9
9.5678
64.5
213
1000
125.89876
33.40
627.87
1.01
9.00
125.90
1000.00
345.00
64.50
213.00
9.57

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Example: The Game of 15

From Prof. Pat Hanrahan's EuroVis'09 keynote talk

  1. There are 2 players

  2. Each player takes a digit in turn

  3. Once a digit is taken, it cannot be used again

  4. The first player to get three digits that sum to 15 wins

{1, 2, 3, 4, 5, 6, 7, 8, 9}

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Why Graphs?

Visualization allows us to summarize information while retaining details...

... as such, it can reveal information that summary statistics may hide

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Example: Anscombe's Quartet

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Example: Datasaurus

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Why Graphs?

Visualization can be faster than your eyes can move!

  • Preattentive features can be detected faster than eye movement (200 ms)
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Example: Preattentive Processing

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How to Make Graphs?

Data -> Mapping -> Visual Representation -> Perception

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How to Make Graphs?

Data -> Mapping -> Visual Representation -> Perception

  • Opportunity + Responsibility
    • We can also easily fool ourselves
    • We need to know how our visual perception works

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Visual Representation

  • Visual variables, marks and channels
  • Their best use and limitations

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Visual Mapping

  • How to best map data features to visual features
  • What options are available (visualization toolbox)
  • How computer algorithms realize the mapping and turn data into images

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Effective Visualization

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Effective Visualization

  • The extent to which it helps people carry out some data analysis or communication tasks better.
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Effective Visualization

  • The extent to which it helps people carry out some data analysis or communication tasks better.
  • Better? Faster, more accurately, increased confidence, more insights, better decisions, etc.
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Effective Visualization

  • The extent to which it helps people carry out some data analysis or communication tasks better.
  • Better? Faster, more accurately, increased confidence, more insights, better decisions, etc.
  • It can be measured only in relation to these tasks and goals.
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Principles of Graphical Excellence

Tufte, E. R. (2018) The visual display of quantitative information. Graphics Press.

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Principles of Graphical Excellence

Tufte, E. R. (2018) The visual display of quantitative information. Graphics Press.

  • Graphical excellence is the well-designed presentation of interesting data—a matter of substance, of statistics, and of design.
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Principles of Graphical Excellence

Tufte, E. R. (2018) The visual display of quantitative information. Graphics Press.

  • Graphical excellence is the well-designed presentation of interesting data—a matter of substance, of statistics, and of design.

  • Graphical excellence consists of complex ideas communicated with clarity, precision, and efficiency.

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Principles of Graphical Excellence

Tufte, E. R. (2018) The visual display of quantitative information. Graphics Press.

  • Graphical excellence is the well-designed presentation of interesting data—a matter of substance, of statistics, and of design.

  • Graphical excellence consists of complex ideas communicated with clarity, precision, and efficiency.

  • Graphical excellence is that which gives to the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space.

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Principles of Graphical Excellence

Tufte, E. R. (2018) The visual display of quantitative information. Graphics Press.

  • Graphical excellence is the well-designed presentation of interesting data—a matter of substance, of statistics, and of design.

  • Graphical excellence consists of complex ideas communicated with clarity, precision, and efficiency.

  • Graphical excellence is that which gives to the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space.

  • Graphical excellence is nearly always multivariate.

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Principles of Graphical Excellence

Tufte, E. R. (2018) The visual display of quantitative information. Graphics Press.

  • Graphical excellence is the well-designed presentation of interesting data—a matter of substance, of statistics, and of design.

  • Graphical excellence consists of complex ideas communicated with clarity, precision, and efficiency.

  • Graphical excellence is that which gives to the viewer the greatest number of ideas in the shortest time with the least ink in the smallest space.

  • Graphical excellence is nearly always multivariate.

  • And graphical excellence requires telling the truth about the data.

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Summary

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Summary

  • A graph

    • is a language to encode information;
    • converts data into direct visual stimuli that do not require "reading";
    • has a purpose, which is to communicate a summary of complex phenomena without giving up on details.
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Summary

  • A graph

    • is a language to encode information;
    • converts data into direct visual stimuli that do not require "reading";
    • has a purpose, which is to communicate a summary of complex phenomena without giving up on details.
  • As a language, it has a series of elements, visual features.
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Summary

  • A graph

    • is a language to encode information;
    • converts data into direct visual stimuli that do not require "reading";
    • has a purpose, which is to communicate a summary of complex phenomena without giving up on details.

  • As a language, it has a series of elements, visual features.

  • We need to learn what's the most appropriate use of such features, and what's the most effective way for mapping data features to visual features.

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Summary

  • A graph

    • is a language to encode information;
    • converts data into direct visual stimuli that do not require "reading";
    • has a purpose, which is to communicate a summary of complex phenomena without giving up on details.

  • As a language, it has a series of elements, visual features.

  • We need to learn what's the most appropriate use of such features, and what's the most effective way for mapping data features to visual features.

  • A good visualization can only be measured in relation to its goals, and the principles of graphical excellence by Tufte are a good starting point as a reference.

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