VII. Design guidelines and ethics in visualization

Edward Tufte: Graphics Excellence, Graphics integrity

• Visual representations of data must tell the truth
• Tufte shows a whole range of graph that either over or underpresent the effects in the data
  • Not telling the truth
  • Misleading charts are oftern done on purpose

6 Principles of graphical integrity

• Principle 1 - Representation of numbers: The representaion of number should be directly proportional to the numerical quantities represented

  → For example: The comparison between 10k and 520k is very misleading

  → How these numbers really look like

  

• Principle 2 - Clear, detailed and thorough labeling: should be used to defeat graphical distortion* and ambiguity

  

  <aside> 🚑

  Graphical distortion: Visual representation of data ≠ numerical representation

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

  </aside>

• Principle 3 - Design and Data Validation: Show data variation, not design variation

  For example: The creator tried to be creative with the chart design but using two different levels of analyses - Yearly and Quarterly - in the same chart can confuse the user.

• Principle 4 - In time-series of money, deflated and standardized units of monetary measurement are better than nominal units

• Principle 5 - Visual Area and Numerical Measure: The number of information-carrying (variable) dimensions should not exceed the number of dimensions in the data
• Principle 6 - Graphics must not quote data out of context.

Data/ink ratio and chart junk

Main Goal: Show data and remove not meaningful graphics

• Maximize the data-ink ratio
• Eraser non-data-ink

→ Strictly related to Principle 3 and Principle 5

Chartjunk - the excessive and uneccesary use of graphical effects in graph

Lie Factor

where

A graph with

• a high lie factor (>1) would exaggerate change in the data it represents
• a small lie factor (>0, <1) would obscure change in the data.

→ A perfectly accurate graph would exhibit a lie factor of 1.

→ Lie factors are clearly a violation of the Principle 1 - The representaion of number should be directly proportional to the numerical quantities represented

3D distortion is misleading

A 3D chart where the depth and perspective distort the perceived size of the bars/pie, misleading the viewer about the actual data values

Y-Axis truncation

If the Y-axis is altered or not starting from zero, exaggerating or compressing data, making the trend appear steeper or flatter than it is.

Logarithm scale

Use of logarithmic scale can be use as well for cheating if not clarified.

→ If the scale is not labeled correctly or the viewer is unaware of the log scale being used, it could cause misinterpretation.

Cumulative plots

Intuitively they are not correctly interpreted: curve rising when data actually decreases with time

→ Wrong unit, as in Principle 4

→ This can lead to a lie factor greater than 1

Choropleth maps and Normalization

Munzner’s rules of thumb

1. No unjustified 3D