North Raleigh Rotarian Katie Turnbull gave a great presentation at our Friday morning extension meeting about data visualization. Katie is a consultant at research and advisory firm, Gartner, Inc.

1. Data Visualization
A (Very) Brief Overview

2. What’s your graphic IQ?
O http://www.perceptualedge.com/files/Grap
hDesignIQ.html

3. What is data viz?
O Data visualization helps us translate numbers
into a picture that we can interpret more
easily.
O Two of the biggest reasons to use data
visualization are to…
O Make sense of data (i.e., help you see patterns)
O Communicate data to others (i.e., executive
presentations)
O Good visualizations allow our eyes to do
some of the heavy lifting in data processing

4. What is data viz?
O The low profit in Q2 is more apparent in
the graph than in the table.
Profit ($M)
Q 1 $4.18
Q 2 $3.24
Q 3 $4.12
Q 4 $3.91
$0 $1 $2 $3 $4 $5
Q1
Q2
Q3
Q4
Profit ($M)

5. Audience matters!
O Visualizations can
be useful, even if
you’re the only one
to see them.
O For presentations,
consider if everyone
will have a printed
copy, or if they need
to be able to see
fine details on a
screen.
Q1 Q2 Q3
Group 1 4.19 4.25 4.50
Group 2 4.00 4.32 4.31
Group 3 4.22 4.18 4.54
Group 4 4.35 4.41 4.62
Q1 Q2 Q3
Group 1 4.19 4.25 4.50
Group 2 4.00 4.32 4.31
Group 3 4.22 4.18 4.54
Group 4 4.35 4.41 4.62

6. Purpose matters!
O Presentations are often expected to
function as both the visual aid during the
meeting, and a reference for those unable
to attend.
O Alternatives:
O 2 documents with difference purposes
O Use “speaker notes”

7. Content matters!
O Different chart types have different
strengths and weaknesses.
O Of the two options below, which do you
think is easier to interpret? Why?
0% 20% 40% 60% 80%
White/Caucasian
Hispanic
Black/African American
Asian
Two or More Races
Prefer not to answer
% of Population% of Population
White/Caucasian
Hispanic
Black/African
American
Asian
Two or More
Races
Prefer not to
answer

8. Types of Data: Comparisons
O Column charts are
likely the best option
if you have few
groups (< 8), but title
length can be a
problem
O Bar charts work
better if you have
more groups or
longer titles
O Heat maps are good
if you’re comparing
more than one group
on more than one
metric

9. Types of Data: Comparisons,
continued
O Bullet graphs have
become popular in
dashboards, since
they’re a compact
option to show a
value against a
specific metric as
well as a showing
what’s considered
good, fair, and bad.
4.18
3.24
4.12
3.91
Q1
Q2
Q3
Q4
Poor Fair Good
2016 2015

10. Types of Data: Composition
75%
67%
82%
73%
13%
11%
12%
18%
12%
22%
Question 1
Question 2
Question 3
Question 4
Fav Neu Unf
O Stacked bar or
column charts are
frequently used for
survey results
O Pie charts can be
used, but be careful
to avoid common
issues with pies
IC
71%
Mgr
26%
Sr Ldr
3% Manager
Status

11. Types of Data: Trend
O Line charts are commonly used to
display long-term trend data.
55%
60%
65%
70%
75%
2014 2015 2016 2017
Group 1
Group 2
Group 3

12. Types of Data: Relationship
O Scatterplots are the
most common graphic to
show relationship data,
but bubble charts can be
used if you need to look
at a third variable
O You can also use line
charts to see
relationships by
comparing the shape of
the graphs
O Network graphs can be
used to show
relationships between
individuals
60%
70%
80%
90%
60% 70% 80% 90%
2017
2016

13. Tips for Useful Charts &
Graphs
O Use the full axis, particularly on column and bar
charts
O Highlight the most important information
O Consider if legends and labels detract from your
point
O This isn’t to say you shouldn’t label your data, but
sometimes it’s redundant or could be placed in a
better way
O Consider the “data-to-ink” ratio
O Pass the “squint” test
O Think about sort order
O Ask for a second opinion

14. Common Problems in
Presentations
O Too much information
O Poor color choices
O Variety for the sake of variety
O Inconsistent axes from one slide to the
next
O Neglecting to label charts
O Not following common conventions

15. Making Bad Charts Better

16. Pretty vs. Useful
Example from: http://viz.wtf/post/147196565281/alphabet-on-the-x-axis-for-reals#notes
O While this chart is pretty and at least
labeled, it’s hard to read quickly. Using an
alphabetic scale on the x-axis doesn’t do
anything to enhance interpretation.

17. Pretty vs. Useful, continued
O This bar chart is a better option for
conveying the same data.
Example from: http://viz.wtf/post/147196565281/alphabet-on-the-x-axis-for-reals#notes

18. Poor Axis Choice
Example from: http://junkcharts.typepad.com/junk_charts/2016/06/what-doesnt-help-readers-on-the-chart-and-what-does-help-off-the-chart.html
The graph below uses a line to show
trend (a common convention), but the
upside-down, truncated y-axis makes it
hard to read. A bar chart version would
be easier to follow, but you could just fix
the y-axis.

19. Republicans are bad at
graphs…
O Media sources with a clear bias are
notorious for using a truncated axis to
their advantage.
6
7.066
0
2
4
6
8
As of 3/27 3/31 Goal
Millions
Obamacare
Enrollment

20. … but so are Democrats
O In addition to
truncating the
axis, this one
also fails to
show that the
upward trend
started before
Obama took
office.
Example from: https://qz.com/580859/the-most-misleading-charts-of-2015-fixed/

21. Yet Another Poor Axis Choice
Example from: https://qz.com/580859/the-most-misleading-charts-of-2015-fixed/
O This is one of those times that it doesn’t
make sense to start the y-axis at 0.

22. Yet Another Poor Axis Choice,
continued
Example from: https://qz.com/580859/the-most-misleading-charts-of-2015-fixed/
O The trend is more apparent when we use
a more realistic axis.

23. How Not to Make a Pie Chart
O Pie charts should never be
used to show values on a
multiple-select item. Use a
bar or column chart instead.
Example from: http://viz.wtf/post/162169270900/what-is-the-recidivism-rate-for-pie-chart
Overall
0%
20%
40%
60%
80%
RecidivismRate
Offense Type

24. How Not to Make a Pie Chart,
continued
O While this pie does add
up to 100%, the design
of the graphic makes it
nearly impossible to
read.
Example from: http://viz.wtf/post/60203066686/the-spiral-staircase-courtesy-of-janwillemtulp
0%
10%
20%
30%
40%
50%
60%
ContrarianThesis
PersonalFailure
SnappyRefrain
Statementof
UtterCertainty
Spontaneous
Moment
OpeningJoke
Sophisticated
VisualAids

25. Telling Your Story
O The headline to go with this chart was “Price has
declined for all products on the market since the
launch of Product C in 2010.”
Example from: http://www.storytellingwithdata.com/blog/2014/05/the-story-you-want-to-telland-one-your

26. Telling Your Story, continued
O Since we’re looking at trend data, a line chart
would make it easier to see where the points are
for each year/product.
Example from: http://www.storytellingwithdata.com/blog/2014/05/the-story-you-want-to-telland-one-your

27. Telling Your Story, continued
O Alternate headline: “As of 2014, retail prices
have converged across products, with an
average retail price of $223, ranging from a low
of $180 (Product C) to a high of $260 (Product
A).
Example from: http://www.storytellingwithdata.com/blog/2014/05/the-story-you-want-to-telland-one-your

28. Use of Color & Number of
Groups
1
1.5
2
2.5
3
3.5
4
4.5
5

29. Use of Color & Number of
Groups, continued
1
1.5
2
2.5
3
3.5
4
4.5
5
1
1.5
2
2.5
3
3.5
4
4.5
5

30. Appendix

31. Chart Chooser
Chart Chooser from: http://extremepresentation.typepad.com/blog/2006/09/choosing_a_good.html

32. Why Are Pie Charts Disliked?
O In each of these charts, can you identify
the largest slice? How does it compare to
the second largest?
Example from: http://prsync.com/oracle/pie-charts-just-dont-work-when-comparing-data---number--of-top--reasons-to-never-ever-use-a-pie-chart--23294/

33. Why Are Pie Charts Disliked?
O Here’s the same data as column charts-
it’s much easier to see differences
between groups.
Example from: http://prsync.com/oracle/pie-charts-just-dont-work-when-comparing-data---number--of-top--reasons-to-never-ever-use-a-pie-chart--23294/

34. If You Really Need to Use a Pie
Chart…
O There are some do’s and don’t’s that are specific
to pies if you really feel you need to use them.
O Arrange the slices in a way that makes sense.
O Don’t use them for more than 2-3 categories.
O Don’t use 3D. Ever.
O Add numeric values as labels so that the end user
doesn’t have to guess. It’s also usually helpful to
put the category in the label instead of using a
legend.
O Don’t “explode” your pies.
O Don’t use pies for questions that allow more than
one response.

35. Excel Tricks
O Trying to get Excel to do something it’s not
really designed to do? Check the Peltier
Tech site.
O https://peltiertech.com/Excel/Charts/ChartI
ndex.html

36. More on Color Choices
O Semantically resonant colors
O https://hbr.org/2014/04/the-right-colors-
make-data-easier-to-read

37. More on Color Choices
O If you know someone in the audience is
color-blind or will be printing the
presentation, there are specific palettes
that are “friendly”.
O http://www.vischeck.com has examples of
what various images look like to individuals
with color-blindness
O http://colorbrewer2.org gives sample
“friendly” palettes

38. Other Resources
There are several great data viz practitioners with
excellent books and websites. Some to look for:
O Stephen Few
O Edward Tufte
O Nathan Yau
O Albert Cairo
O Cole Nussbaumer
Knaflic
O Junk Charts
http://junkcharts.typepad.com/
O WTF Visualizations
http://viz.wtf/