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Data Visualization The Good, the Bad, the Weird
Nam Wook Kim Mini-Courses — January @ GSAS 2018
Will Start at 2:35 pm Data Visualization The Good, the Bad, the - - PowerPoint PPT Presentation
Will Start at 2:35 pm Data Visualization The Good, the Bad, the - - PowerPoint PPT Presentation
Will Start at 2:35 pm Data Visualization The Good, the Bad, the Weird Nam Wook Kim Mini-Courses January @ GSAS 2018 Goal Rules of thumbs to critique visualization design 45 Ways to Communicate Two Quantities [Santiago Ortiz 2012]
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Goal
Rules of thumbs to critique visualization design
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45 Ways to Communicate Two Quantities
[Santiago Ortiz 2012]
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Which one is the best and why?
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There are numerous ways to draw even just two numbers…
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Is there an ideal way to visualize a data set?
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It depends on
Data types e.g., table, network, spatial, temporal Context of the data Tasks to perform e.g., identify trends, compare values Questions to answer Messages to deliver
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But, is there at least a guide for visualization design?
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Edward Tufte’s Design Principles
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Graphical Integrity
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Flowing data
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Flowing data
Bar Chart should have a zero-baseline. Because you are comparing the lengths
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Flowing data
Or comparing positions from the baseline.
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Do we always need a zero-baseline?
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Flowing data
Line Chart may not have a zero-baseline. Because you are comparing the angle
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Line chart’s aspect ratios can matter too.
https://eagereyes.org/basics/banking-45-degrees
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Line chart’s aspect ratios can matter too.
A rule of thumb is banking to 45 degrees to minimize errors in visual judgments of slope ratios.
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Comes down to the message you want to deliver
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RANDOM QUARTER
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INCORRECT Y-SCALE 2 mil 172 pixels 138 pixels 4.5 mil
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15 MIL JOB LOSS? MISLEADING TITLE
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The truth is…
SOURCE: Worst chart I've seen all day, Jocelyn Fong (2010)
unemployed not job loss! stabilized after 2009
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what is depicted in the previous one.
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Partial data
http://www.motherjones.com/kevin-drum/2012/01/lying-charts-global-warming-edition/
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Show data in context
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Average Annual Global Temperature (℉) 1880-2015
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Choose axis scales wisely.
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Tell the Truth!
The representation of numbers … should be directly proportional to the numerical quantities measured. — Edward Tufte 1983
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Lie Factor
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Lie Factor = Size of effect in graphic Size of effect in data
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Lie Factor = Size of effect in graphic Size of effect in data Size of effect = Percentage change | V1 — V2 | = | V1 |
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Year Standard MPG
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This line, representing 18 miles per gallon in 1978, is 0.6 inches long
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This line, representing 18 miles per gallon in 1978, is 0.6 inches long This line, representing 27.5 miles per gallon in 1985, is 5.3 inches long
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This line, representing 18 miles per gallon in 1978, is 0.6 inches long This line, representing 27.5 miles per gallon in 1985, is 5.3 inches long Lie Factor = (5.3-0.6) / 0.6 (27.5-18) / 18 = 14.8
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This chart uses radius of the balloon to encode the data Doubling the radius (or data) increases the perceived area by four. Lie factor = (4-1)/(2-1) = 3.
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The size of the balloon should be something like this.
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Avoid Distortion!
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Maximize Data-Ink Ratio
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Data-Ink Ratio = Data-Ink Total Ink in Graphic
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Stephen Few (2011)
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Avoid Chart Junks
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Chart Junks = Unnecessary visual elements in charts that distracts the viewer from the information
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Are these chart junks?
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Not all chart junks are the same.
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Useful chart junks?
Source: Useful Junk? The Effects of Visual Embellishment on Comprehension and Memorability of Charts, CHI’10.
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Not harmful in comprehension but more engaging & memorable
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“The same ink should often serve more than
- ne graphical purpose. A graphical element
may carry data information and also perform a design function usually left to non-data-ink.” — [Edward Tufte 83]
Replace with an aesthetic function? SLIDE 71
Haroz et al. CHI’15
Contextual representation can be helpful
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Pie Charts
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[Schutz 2007]
Challenge: Find the biggest pie slice in each pie chart!
Ask the second choice SLIDE 74
[Schutz 2007]
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Share of Coverage by Topic on TechCrunch
[http://www.storytellingwithdata.com/blog/2011/07/death-to-pie-charts]
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Share of Coverage by Topic on TechCrunch Too many slices! Too many colors! Bad color contract!
[http://www.storytellingwithdata.com/blog/2011/07/death-to-pie-charts]
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?!
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Math fail?!
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World’s Most Accurate Pie Chart
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Some rules of thumb
- You're comparing the parts to the whole.
- There's a small number of slices.
- Sort the values.
- Start at 12 o’clock.
- Use alternatives (e.g., bar chart)
Source: https://eagereyes.org/pie-charts
Pie charts are space efficient though
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Rainbow Colormap
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[http://factmyth.com/factoids/visible-light-is-electromagnetic-radiation/]
The rainbow color map is based
- n the order of colors in the the
visible light spectrum.
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Can you say which color represents a higher or lower value group?
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How The Rainbow Color Map Misleads (Kosara 2013)
Luminance Hue
Lack of perceptual ordering
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Example: How many low ESS regions found?
39% 71% 10.2 sec/region 5.6 sec/region
ESS: Endothelial shear stress [M. Borkin et al 2011]
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Some rules of thumb
Qualitative (rainbow) scheme — categorical data. Sequential scheme — ordered categories or numerical data Diverging scheme — numerical data with a meaningful mid-point.
[Color Brewer]
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3D charts
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Perspective distorts information
2D is more accurate and efficient in identifying problematic regions.
71% 91% 2.4 sec/region 5.6 sec/region
[M. Borkin et al 2011]
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Perspective distorts information
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Can rotate, but still no picture at once.
Occlusion hides information
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Exploring and Reducing the Effects of Orientation on Text Readability in Volumetric Displays (CHI 2007)
Tilted text isnʼt legible
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Depth judgment is bad
Human underestimate depth! Actual intensity change vs Perceived Sensation
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External cognition vs Internal cognition
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Eyes beats memory
http://www.randalolson.com/2015/08/23/small-multiples-vs-animated-gifs-for-showing-changes-in-fertility-rates-over-time/
Harder to compare visible item to memory of what you saw Animation
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Use external cognition over internal cognition
Eyes beats memory
Easy to compare by moving eyes between side-by-side views Small multiples
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Tufte Principles Other Considerations
- Graphical integrity
- The lie factor
- Maximize data-ink ratio
- Avoid harmful chart junk
- Pie charts
- Rainbow colormap
- 3D charts
- Eyes beats memory
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Subjective Dimensions
Aesthetics: Attractive things are perceived as more useful. Style: Communicates brand, process, who the designer is. Playfulness: Encourages experimentation and exploration. Vividness: Can make a visualization more memorable.
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Subjective Dimensions
Aesthetics: Attractive things are perceived as more useful. Style: Communicates brand, process, who the designer is. Playfulness: Encourages experimentation and exploration. Vividness: Can make a visualization more memorable.
Important if you want others to look at your chart!
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Where is a red circle?
Graphical Perception
Next
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