the visual display of quantitative data joyce chapman, consultant for communications & data...

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


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Pre-attentive attributes

Attributes of form

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Attributes of color

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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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Very precise quantitative perception

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Less precise quantitative perception

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Scatterplots take advantage of 2D spatial positioning

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Line charts also take advantage of 2D spatial positioning

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Bar charts take advantage of 2D spatial positioning (the end of each bar) and line length

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The humble pie chart

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The humble pie chartWhich is larger, B or D?

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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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Points

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Lines

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Lines

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Bars

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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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Nominal comparison


Categorical subdivisions have no connection

Values are discrete

Aims to highlight relative size

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Nominal comparison

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Time series


?

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Time series


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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Time series

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Correlation


?

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Correlation


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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Parts-to-whole


?

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Parts-to-whole


Discrete value comparison Individual bars are better than stacked bars

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Parts-to-whole

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Parts-to-whole

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Deviation


?

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Deviation


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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Deviation

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Distribution


?

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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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Histograms: distribution

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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 [email protected]

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: [email protected]

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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the visual display of quantitative data joyce chapman, consultant for communications & data...

Documents

visual attributes

preattentive processing

quantitative values

graph type lines

precise values

graph type bars

graph type points

individual values