iat 355 visual analytics encoding information: design · lines encourage trends iat 355 | design...

IAT 355 Visual Analytics

Encoding Information: Design Lyn Bartram

4 stages of visualization design

IAT 355 | Design Idioms 2

Recall: Data Abstraction

•  Tables •  Data item (row) with attributes (columns) : row=key, cells = values

•  Networks •  Item (node) with attributes (features) and relations (links) •  Trees (hierarchy) •  Node = key, node-node, link = key, cell = value

•  Text/Logs •  Grammar •  Bag of words •  Derived values

•  Image •  2d location = key, pixel value expresses single attribute or combo of attributes

according to coding (RGB)


A Framework for Analysis (Munzner)


Design IDIOM

Visualization: Why?

Analyze, Explore, Discover

Explain, Illustrate, Communicate


Munzner


Why does not define how completely


Designing Vis Idioms (Munzner)


Review: (Munzner)

•  Marks Points Lines Areas

•  Channels Position hue Size saturation Shape lightness orientation texture …


What is this? How Much/many of something is there?

Credit: T. Munzner, 2014

Fundamental principles

Expressiveness: •  the visual encoding should express all of, and only, the

information in the dataset attributes

Effectiveness: •  the importance of the attribute should match the

salience of the channel. •  Use the strongest and most accurate channels for the

most important interpretation tasks (data)


Space


Slide adapted from David Lippman's

Perfect positive Strong positive Positive correlation r = 1 correlation r = 0.99 correlation r = 0.80

Strong negative No Correlation Non-linear correlation r = -0.98 r = 0.16 relationship

However …

•  Scatter plots can be difficult to understand

•  What alternatives are there?

•  More generally, what kinds of techniques are best for what kinds of problems?

Scatterplot as idiom


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Circumference (ft)

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ht (f

t)

Bar chart idiom

•  Categorical attributes match well with spatial regions

•  Separate, order, align



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Few’s correlation bar graph

Paired Bar graph with trend lines (Few)

Line Chart idiom

•  Line charts, dotplots •  Good for ordered data

IAT 355 | Design Idioms


Mind the Gap - An Economic Chart Remake

What’s wrong?


Lines encourage trends


Je Zacks and Barbara Tversky. Bars and Lines: A Study of Graphic Communication." Memory and Cognition 27:6(1999), 1073{1079

Lines imply connections •  “the more male someone is the

taller he is”

Use when there is some ordered progression between the discrete categories on the x-axis •  “12 year olds are taller than 10

year olds”

Tufte’s Sparklines

•  Give a hint of the trend, but don’t show the actual axes and scales.

peer2patent.org

•  Good for dashboards and small spaces

Lines: Aspect ratio matters!

•  our ability to judge angles is more accurate at exact diagonals than at arbitrary direction •  We can judge distances “off” 45 or 90 degrees (43 ) but cannot see

the difference between 20 and 22 degrees •  Multiscale banking to 45 degrees – algorithm to compute informative

aspect ratios to maximise line segments close to the diagonal


What about Pies?

Radial layouts


radial idioms


Idiom Star plot

What:data Table: 1 quant value, 1 categorical attribute

How: Encode length coding along point marks at 1D spatial position along axis + 1D spatial position for aligned axes

Idiom Pie chart

What:data Table: 1 quant value, 1 categorical attribute

How: Encode area and angle

Percent Blue rela,ve to Red?

Percent Blue rela,ve to Red?

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Few’s criteria for an effective visualization

•  Clearly indicate the nature of the relationship •  Represent the quantities accurately •  Makes it easy to compare the quantities •  Makes it easy to see the ranked order of values •  Makes obvious how people should use the information

Clearly indicate the nature of the relationship?

Represents quantities accurately?

Makes it easy to compare quantities?

Makes it easy to see ranked values?

Makes it easy to see how people should use information?

A better way

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body

brain

blood

Percent Water

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body brain blood

Percent Water

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body brain blood

Percent Water

Even Be>er*

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Too Little

About Right

Too Much

National Spending to Deal with Drug Addiction

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Too Little

About Right

Too Much


Male

Female

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Too Little

About Right

Too Much


Female Male

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Male

Female


Too Little

About Right

Too Much

h>p://chartchooser.juiceanaly,cs.com/

Colour

Get it right in black & white

•  Value •  Perceived lightness/darkness •  Controlling value primary rule for design

•  Value defines shape •  No edge without lightness difference •  No shading without lightness variation

•  Value difference (contrast) •  Defines legibility •  Controls attention •  Creates layering


Controls Legibility


colorusage.arc.nasa.gov

54

Legibility


Drop Shadows

Drop Shadow Drop shadow adds edge Primary colors on black

Primary colors on black





Primary colors on white






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Readability


If you can’t use color wisely, it is best to avoid it entirely Above all, do no harm

If you can’t use color wisely, it is best to avoid it entirely Above all, do no harm.

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Why does the logo work?


Why does this logo work so well?


Value control

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Contrast and Layering

•  Value contrast creates layering


Context

Context

Normal

Normal

Urgent Context

Context

Normal

Normal

Urgent Context

Context

Normal

Normal

Urgent

colorusage.arc.nasa.gov

59

What Defines Layering?

•  Perceptual features •  Contrast (especially lightness) •  Color, shape and texture

•  Task and attention •  Attention affects perception

•  Display characteristics •  Brightness, contrast, “gamma”


Emergency

Emergency

Emergency

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General guidelines … or from Tufte to practice [Stone, Ware]

•  Assign colour according to function •  Use contrast to highlight •  Use analogy to group

•  Control value contrast for legibility •  Break isoluminance with borders


From principles to palettes

•  Limit palette to 2 or 3 colours and use variations within them

•  Different choices convey different messages


Tableau Color Example

•  Color palettes •  How many? Algorithmic? •  Basic colors (regular and pastel) •  Extensible? Customizable?

•  Color appearance •  As a function of size •  As a function of background

•  Robust and reliable color names


Tableau™ Colors


www.tableausoftware.com

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Maximum hue separation


Analogous, yet distinct


Sequential


Stephen Few’s practical rules on colour

1.  If you want different objects of the same color in a table or graph to look the same, make sure that the background—the color that surrounds them—is consistent.

2.  If you want objects in a table or graph to be easily seen, use a background color that contrasts sufficiently with the object.


Don’t do this!

69

Few (2)

3. Use colour only when needed to serve a particular communication goal

4. Use different colours only when they correspond to differences of meaning in the data


Few (3)

5. Use soft, natural colors to display most information and bright and/or dark colors to highlight information that requires greater attention.

6. When using color to encode a sequential range of quantitative values, stick with a single hue (or a small set of closely related hues) and vary intensity from pale colors for low values to increasingly darker and brighter colors for high values.


Few (4)

7. Non-data components of tables and graphs should be displayed just visibly enough to perform their role, but no more so, for excessive salience could cause them to distract attention from the data

8. Avoid using red/green display without redundant cueing 9. Avoid using visual effects in graphs


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