visualization basics cs 5764: information visualization chris north
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Visualization Basics
CS 5764: Information Visualization
Chris North
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Review
• What is the purpose of visualization?
• How do we accomplish that?
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Basic Visualization Model
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Goal
Data
Data transfer
Insight(learning, knowledge extraction)
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Method
Data
Visualization
Map: data → visual
~Map-1: visual → data insight
Data transfer
Insight
Visual transfer
(communication bandwidth)
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Visual Mappings
Data
Visualization
Map: data → visual
Visual Mappings must be:• Computable (math)
visual = f(data)
• Comprehensible (invertible)data = f-1(visual)
• Creative!
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PolarEyes
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Visualization Pipeline
Raw data(information)
Visualization(views)
Data tables
Visualstructures
Datatransformations
Visualmappings
Viewtransformations
task
User interaction
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Data Table: Canonical data model
• Visualization requires structure, data model
• (All?) information can be modeled as data tables
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Data TableAttributes (aka: dimensions, variables, fields, columns, …)
Items
(aka: tuples, cases, records, data points, rows, …)
ValuesData Types:•Quantitative•Ordinal•Categorical•Nominal
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Attributes
• Dependent variables (measured)
• Independent variables (controlled)
ID Year Length Title
0 1986 128 Terminator
1 1993 120 T2
2 2003 142 T3
… … … …
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Data Transformations
• Data table operations:• Selection
• Projection
• Aggregation– r = f(rows)
– c = f(cols)
• Join
• Transpose
• Sort
• …
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Visualization Pipeline
Raw data(information)
Visualization(views)
Data tables
Visualstructures
Datatransformations
Visualmappings
Viewtransformations
task
User interaction
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Visual Structure
• Spatial substrate
• Visual marks
• Visual properties
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Visual Mapping: Step 1
1. Map: data items visual marks
Visual marks:• Points
• Lines
• Areas
• Volumes
• Glyphs
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Visual Mapping: Step 2
1. Map: data items visual marks
2. Map: data attributes visual properties of marks
Visual properties of marks:• Position, x, y, z
• Size, length, area, volume
• Orientation, angle, slope
• Color, gray scale, texture
• Shape
• Animation, blink, motion
•
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Example: Spotfire
• Film database• Film -> dot
– Year x
– Length y
– Popularity size
– Subject color
– Award? shape
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Visual Mapping Definition Language
• Films dots• Year x
• Length y
• Popularity size
• Subject color
• Award? shape
• Mathematically, how to map: Year x ?
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E.g. Linear Encoding
• year x
x – xmin year – yearmin
xmax – xmin yearmax – yearmin
yearmin
xmin
yearmax
xmax
yearx
=
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The Simple Stuff
• Univariate
• Bivariate
• Trivariate
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Univariate
• Dot plot
• Bar chart (item vs. attribute)
• Tukey box plot
• Histogram
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Bivariate
• Scatterplot
•
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Trivariate
• 3D scatterplot, spin plot
• 2D plot + size (or color…)
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The Challenges?
•
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The Challenges?
• Evaluate or compare designs?
• Effectiveness?
• Data transformations, whats the right data table?
• More data, multidimensional
• Too many dots, limited space
• Choosing which data?
• Semantics
• System limitations
• …
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Some Visualization Design
Principles
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Getting Started
1. Start with Overview
2. Choose visual encodings
3. Consider interaction
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1. Start with Overview: Design for Insight
• Avoid the temptation to design a form-based search engine• More tasks than just “search”
• How do I know what to “search” for?
• What if there’s something better that I don’t know to search for?
• Hides the data
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Information Visualization Mantra
(Shneiderman)
• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand• Overview first, zoom and filter, then details on demand
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Cost of Knowledge / Info Foraging
(Card, Piroli, et al.)
• Frequently accessed info should be quick• At expense of infrequently accessed info
• Bubble up “scent” of details to overview
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Increase Data Density
• Calculate data/pixel
“A pixel is a terrible thing to waste.”
(Tufte)
(Shneiderman)
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Eliminate “Chart Junk”
• How much “ink” is used for non-data?
• Reclaim empty space (% screen empty)
• Attempt simplicity(e.g. am I using 3djust for coolness?)
(Tufte)
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2. Choose Visual Encodings
(Mackinlay)
• Expressiveness• Encodes all data
• Encodes only the data
• Effectiveness• Cleveland’s rules
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Ranking Visual Properties
1. Position
2. Length
3. Angle, Slope
4. Area, Volume
5. Color
Design guideline:• Map more important data attributes
to more accurate visual attributes (based on user task)
Increased accuracy for quantitative data
(Cleveland and McGill)
Categorical data:1. Position2. Color, Shape3. Length4. Angle, slope5. Area, volume(Mackinlay hypoth.)
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Example• Hard drives for sale: price ($), capacity (MB), quality rating (1-5)
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3. Consider Interaction
• For un-represented data• Direct Manipulation (Shneiderman)
• Visual representation
• Rapid, incremental, reversible actions
• Pointing instead of typing
• Immediate, continuous feedback
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Break out of the Box
• Resistance is not futile!• Creativity; Think bigger, broader• Does the design help me explore, learn, understand?• Reveal the data
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Class Motto
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Class Motto
Show me the data!
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Visualization Design
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HCI Design Process
• Iterative, progressively concrete
1. Analyze 3. Evaluate2. Design
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HCI UI Evaluation Metrics
• User learnability:• Learning time• Retention time
• User performance: ***• Performance time• Success rates• Error rates, recovery• Clicks, actions
• User satisfaction:• Surveys
Not “user friendly”
Measure while users perform benchmark tasks
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Visualization Design
• Analyze problem:• Data: schema, structures, scalability• Tasks/insights• Prioritize tasks and data attributes
• Design solutions:• Data transformations• Mappings: data→visual• Overview strategies• Navigation strategies• Interaction techniques• multiple views vs. integrated views
• Evaluate solutions:• Analytic: Claims analysis, tradeoffs• Empirical: Usability studies, controlled experiments
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1. Analyze the Problem
• Data:• Information structure
• Scalability***
•
• Users:• Tasks
•
•
• Existing solutions (literature review)
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Information Structures
• Tabular: (multi-dimensional)
•
• Spatial & Temporal: • 1D:
• 2D:
• 3D:
• Networks:• Trees:
• Graphs:
• Text & Documents:•
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Data Scalability
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Data Scalability
• # of attributes (dimensionality)
• # of items
• Value range(e.g. bits/value)
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User Tasks• Easy stuff:
• Reduce to only 1 data item or value• Stats: Min, max, average, %• Search: known item
• Hard stuff:• Require seeing the whole• Patterns: distributions, trends, frequencies, structures• Outliers: exceptions• Relationships: correlations, multi-way interactions• Tradeoffs: combined min/max• Comparisons: choices (1:1), context (1:M), sets (M:M)• Clusters: groups, similarities• Anomalies: data errors• Paths: distances, ancestors, decompositions, …
Forms can do this
Visualization can do this!
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3. Evaluate Claims Analysis:
• Identify an important design feature• + positive effects of that feature
• - negative effects of that feature
• Identify a design dimension• Identify designs alternatives
• +/- tradeoff effects
Tradeoff Analysis:
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Exercise: Pie vs. Bar
• Data: population stats
• Scalability? Effectiveness for Tasks?
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Pie vs. Bar• Scalability: state and pop
overloaded on circumf.
•
• state on x, pop on y•
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Stacked BarAKALAR
CACO
…
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Upcoming
• Tabular (multi-dimensional)
• Spatial & Temporal • 1D / 2D
• 3D
• Networks• Trees
• Graphs
• Text & Docs
• Overview strategies• Navigation strategies• Interaction techniques
• Development• Evaluation