SLIDE 1 Vis is10 101 - Vi
Visu sual aliz izat atio ion
Lecture 6: The Visualization Alphabet: Marks and Channels
SLIDE 2 This Week
Homework 1! Lecture 5: Lecture 6: Section 2: Reading:
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No Device Policy
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Last Week
SLIDE 5 Terms
Dataset Types Data Types
SLIDE 6 Tables
Flat Table Multidimensional Table
Keys Attributes Item Values
SLIDE 7 Multidimensional Tables
z
Keys: Genes Keys: Patients
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Graphs/Networks
SLIDE 9 Fields
Attribute values associated with cells Cell contains data from continuous domain Measured or simulated Sampling & Interpolation
SLIDE 10 Other Collections
Sets Lists Clusters
SLIDE 11 Data Types
Nominal (labels) Ordinal (ordered) Interval (location of zero arbitrary) Ratio (zero fixed)
On the theory of scales and measurements [S. Stevens, 46]
SLIDE 12 Item/Element/ (Independent) Variable
SLIDE 13 Attribute/ Dimension/ (Dependent) Variable/ Feature
SLIDE 16 Attribute Types?
SLIDE 17 Categorical Ordinal Quantitative
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Design Critique
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Recalled Cars NY Times
http://goo.gl/tDVISB
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The Visualization Alphabet: Marks and Channels
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Marks & Channels
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Example: Homework 2
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Marks for Items
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Marks for Links
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Containment can be nested
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Channels (aka Visual Variables)
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Jacques Bertin
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Bertin’s Visual Variables
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Using Marks and Channels
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Redundant encoding
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Good bar chart?
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Types of Channels
SLIDE 34 Channels: Expressiveness Types and Effectiveness Ranks
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What visual variables are used?
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What visual variables are used?
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Characteristics of Channels
Selective Associative Quantitative (Magnitude vs Identity Channels)
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Characteristics of Channels
Order (Magnitude vs Identity) Length
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Position
Strongest visual variable Suitable for all data types Problems:
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Example: Scatterplot
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Position in 3D?
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Length & Size
Good for 1D, OK for 2D, Bad for 3D Easy to see whether one is bigger Aligned bars use position redundantly
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Example 2D Size: Bubbles
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Value/Luminance/Saturation
OK for quantitative data when length & size are used. Not very many shades recognizable
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Example: Diverging Value-Scale
SLIDE 46 Color
Good for qualitative data (identity channel) Limited number of classes/length (~7-10!) Does not work for quantitative data! Lots of pitfalls! Be careful! Suggested rule:
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Color: Bad Example
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Color: Good Example
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Shape
Great to recognize many classes. No grouping, ordering.
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Chernoff Faces
Idea: use facial parameters to map quantitative data
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More Channels
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Why are quantitative channels different?
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Steven’s Power Law, 1961
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How much longer?
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How much longer?
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How much steeper?
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How much larger (area)?
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How much larger (area)?
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How much larger (diameter)?
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How much darker?
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Position, Length & Angle
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Other Factors Affecting Accuracy
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Cleveland / McGill, 1984
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Heer & Bostock, 2010
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Jock Mackinlay, 1986
SLIDE 68 Channels: Expressiveness Types and Effectiveness Ranks
SLIDE 69 Next Week
Lecture 7: Lecture 8: Section 3: Homework 1 due to Friday, 30 October.