the visual display of quantitative data joyce chapman, consultant for communications & data...
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The visual display of quantitative data
Joyce Chapman, Consultant for Communications & Data AnalysisState Library of North Carolina, 6-11-2014
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AgendaVisual perception and quantitative communicationFundamental concepts of graphsGeneral design for communication
This webinar will be recorded and made available here:http://statelibrary.ncdcr.gov/ld/webinars.html
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What is the message?
Visual perception and quantitative communication
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Stimulus Stimulation Perception
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Pre-attentive processing
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Extremely fast, pre-conscious visual processing
Pre-attentive processing
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Pre-attentive processing
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Pre-attentive attributes
Attributes of form
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Pre-attentive attributes
Attributes of color
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Pre-attentive attributes
Attributes of spatial position and motion
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But which of these visual attributes can be used to encode quantitative
information?
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Pre-attentive attributes
Very precise quantitative perception
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Pre-attentive attributes
Less precise quantitative perception
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Pre-attentive attributes
Scatterplots take advantage of 2D spatial positioning
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Pre-attentive attributes
Line charts also take advantage of 2D spatial positioning
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Pre-attentive attributes
Bar charts take advantage of 2D spatial positioning (the end of each bar) and line length
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Pre-attentive attributes
The humble pie chart
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Pre-attentive attributes
The humble pie chartWhich is larger, B or D?
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Pre-attentive attributes
Some limitations of our brains
Up to 8 different huesUp to 4 different orientations or sizesLess than 10 of other attributesWe can only process one attribute at a time
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Fundamental concepts of graphs
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TableA structure for organizing and displaying
information. Quantitative values are encoded as text.
GraphA visual display of quantitative information.
Quantitative values are encoded as visual objects.
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When to use tables When you will need to look up individual values
When you will need to compare individual values
When precise values are required
When the quantitative information to be communicated involves more than one unit of measure
When to use graphs When the message is contained in the shape of values
To reveal relationships among multiple values
When there is a large amount of data to distill25
How to choose a graph type
Different types of quantitative relationships require different forms of graphs
Points
Lines
Bars
Shapes with 2D area
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How to choose a graph type
Points
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How to choose a graph type
Lines
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How to choose a graph type
Lines
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How to choose a graph type
Bars
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How to choose a graph type
2D area
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Relationships in graphs1.Nominal comparison2.Time series3.Correlation4.Part-to-whole5.Deviation6.Distribution
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Relationships in graphs
Nominal comparison
Points lines bars 2D area
?
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Relationships in graphs
Nominal comparison
Points lines bars 2D area
Categorical subdivisions have no connection
Values are discrete
Aims to highlight relative size
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Relationships in graphs
Nominal comparison
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Relationships in graphs
Time series
Points lines bars 2D area
?
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Relationships in graphs
Time series
Points lines bars 2D area
Our culture visualizes time as linear and left to right The visual weight of bars detracts from message in
the shape of the data Points don’t work because dots floating in space
cannot denote the sequential nature of time
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Relationships in graphs
Time series
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Relationships in graphs
Correlation
Points lines bars 2D area
?
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Relationships in graphs
Correlation
Points lines bars 2D area
Must show two sets of quantitative values in relation to each other instead of one
Both X and Y axis provide quantitative scales
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Relationships in graphs
Parts-to-whole
Points lines bars 2D area
?
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Relationships in graphs
Parts-to-whole
Points lines bars 2D area
Discrete value comparison Individual bars are better than stacked bars
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Relationships in graphs
Parts-to-whole
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Relationships in graphs
Parts-to-whole
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Relationships in graphs
Deviation
Points lines bars 2D area
?
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Relationships in graphs
Deviation
Points lines bars 2D area
Usually teamed with another relationship When combined with time-series, lines are best When combined with anything else or standing
alone, bars are usually used.
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Relationships in graphs
Deviation
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Relationships in graphs
Distribution
Points lines bars 2D area
?
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Relationships in graphs
Distribution
Points lines bars 2D area boxplots
The shape of the distribution is most important Consider whether you have one or many
distributions (lines for multiple, histogram for single)
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Relationships in graphs
Histograms: distribution
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Relationships in graphs
Box plots: distribution
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General design for communication
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"Above all else show the data." –
Edward Tufte
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Data-ink ratio
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Data-ink ratio
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Data-ink ratio
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Who, what, where, when?
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Create by the News & Observer, 4-12-2014Contact jane.doe@no.org
Figure 1.
Avoid “Chart junk”: 3D effects for non-3D data
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Maintain visual correspondence to quantity
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eeeUse zero-based
scales How much more satisfied were patrons at the Lilly library than the Iris library?
With the baseline at zero
How much more satisfied were patrons at the Lilly library than the Iris library?
Concepts and charts for this presentation were borrowed from this book
Few, Stephen. (2004). Show me the numbers: designing tables and graphs to enlighten.
Further reading, if you’re interested Few, Stephen. (2009). Now you see it: simple visualization
techniques for quantitative analysis.
Tufte, Edward. (1983). The Visual Display of Quantitative Information.
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Questions?
Contact: joyce.chapman@ncdcr.gov919-807-7421
Find this Powerpoint and recorded webinar here: http://statelibrary.ncdcr.gov/ld/webinars.html
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To find out about continuing education opportunities offered by the State Library:
Join the CE listserv: https://lists.ncmail.net/mailman/listinfo/ceinfo
Sign up for email updates from the State Library blog: http://statelibrarync.org/ldblog/
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Example:How could this chart be improved?
Find more examples here: http://www.perceptualedge.com/exampl
es.php64
Fix this chart
Executives want to understand both the range of selling prices and the mean selling prices over 12 months.
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Fix this chart
Executives want to understand both the range of selling prices and the mean selling prices over 12 months.
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