Common Mistakes In Data Visualization

Common mistakes in data visualization Amedee Van Gasse BarCampGhent3 19 December, 2009

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The power of data visualization
Chinese proverb: One Picture is Worth Ten Thousand Words
The Fast-Food Information Age
Pr0n for the stats junk
Pointy-Haired Boss
Twitter: Infograph of the day ( @bnox )

What Makes Good Information Design?
Interestingness
Function
Form
Integrity

With Great Power...
... Comes Great Responsibility
Look for the Hidden Agenda
Trust No One
Lies, Damned Lies, and Statistics

Let's just face it:

Why do we lie?
Charts, infographics,... are only a simplified representation of a complex reality
Compare with maps: they are also (white) lies
Used to convice others
Because it looks cool
Because we don't know any better

The axis are (not) your allies
Y axis starts at 500. Why 500?
Gradients
Grey on grey
Original chart has animation...

Why?
December = 1/5 size of January = CRISIS!!!
Fear, Uncertainty and Doubt
Convince employees of needed budget cuts
Or... just blind faith in Excel???

What really happened
2008 up to Q3 was an exceptionally good year
Yes, there was a crisis, but...
We went to 1/2, not to 1/5
Excel bug: lowest value on Y-axis is ”magic”...

What we saw in the meeting 47.988 47.115 47.385 2008 OB 2009
No scale
Why start at 40.000? Why not 30.000 or 45.000?
3D adds no value
versus 2008: - 1,3 % versus OB : + 0,6 %

A more accurate version
Scale added
Starts at 0
No 3D
versus 2008: - 1,3 % versus OB : + 0,6 %

You need X-Ray Vision for this one
Confession: I made this one
What if executed > planned? -> invisible!
Better chart: bars (executed) + lines (planned)

Pie chart hell
I made these too!
3D
Gradients
Could have been combined with previous chart

Combining the two previous charts

The donut: evil twin of the pie
Psychedelic
Hard to compare series

Can't get enough pie?
Only one thing is worse than one pie: two pies
Little information
You can tell your story with one chart

”Pies are to scale”
Pretty colors
3D: same diameter?Perspective?

The Mother of all Pie Charts
http://www.slideshare.net/netlash/old-media-vs-new-media
Sorry, @netlash , but this one really sucks
Why are Greece and Germany the same size?
Red = good or bad?
Lots of comments on InformationIsBeautiful.net

The original chart
Boring
Ugly
Easy to understand

By the way, did I already tell you that I really hate pie charts?

The only good pie charts Pac Man Pie: @flexyflow

Want to see some more silly charts?

Spiderman loves this one!
Radar chart
Hard to read
Needs a lot of tweaking
Ugly even with perfect data

3D: Manhattan chart
You can always go... downtown ♫

3D: unstacked area chart
This one comes with X-Ray glasses
Can you see S3 (yellow)?
Use a 2D line chart!

Some practical tips
Colors
Axes, legend & title
Logarithmic scale

Colors
No gradients in background
Background contrasts with objects
Use color only when needed
Different color = difference of meaning in data
Soft colors + bright/dark for highlights

Colors
Stick with a single hue
Non-data just visible enough
Avoid red+green (colorblind)
Leave special effects to Hollywood!!!

And the Oscar goes to...

Axes, legend & title
X Axis: Category or Value?
Line charts or XY Scatter charts?
Zero-based or not?
Second Y axis?
Good title and axis labels = no legend needed
If your chart needs a legend, it is a bad chart

Axes gone wrong
X axis is time + location
X and Y axes ar not linear
A (bad) joke from http://graphjam.com

Logarithmic scale
Nonlinear stimulus-response: 10x pay raise makes you only 2x happier
Avoid unless you know what you are doing
Can't be used with 0 in data
Use a trick: add 0.001

General tips
What is your message?
Who is your audience?
Prepare your data
Don't have blind faith in your software

Links http://peltiertech.com/WordPress/category/chart-busters http://chandoo.org/wp/category/visualization/ http://graphjam.com/ http://www.informationisbeautiful.net/ http://www.smashingmagazine.com/2009/09/11/ 25-useful-data-visualization-and-infographics-resources/ http://www.smashingmagazine.com/2007/08/02/ Data-visualization-modern-approaches/

Common Mistakes In Data Visualization

by Amedee Van Gasse on Dec 27, 2009

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