Module 6 - Complex Idioms

Question 1

Why Maps? (V1)

Answer 1

1. Understanding spatial relationships
2. Familiarity
   * People know where something is on a map
   (assuming they are familiar with the region)
3. Maps act as an index from spatial to semantic information and vice-versa.

Question 2

Choropleth map (V1)

Answer 2

Data = 1 Quantitative attribute w/ geographic geometry
Mark = Geometric Area
Channel = Color
Tasks = Spatial relationship

*misleading (size of objects depend on geography, not the attribute), cannot compare well
-> resolve by using glyphs
mark = dot/point
channel = size

Question 3

Cartogram (V1)

Answer 3

a map that distorts such that area represents size/quantity correctly
*distorting and accuracy at the cost familiarity

Question 4

Dot Map (V1)

Answer 4

Introduce a point that represents observations, and scatter across map

Question 5

Density Map (V1)

Answer 5

Turn discrete data into continuous data (using KDE) and plot as a heatmap

Can also be 2d, with transparency representing bins

Question 6

Topographic Map (V1)

Answer 6

Data = Scalar Spatial Field (quantitative continuous data, can interpolate between points) w/ geographic geometry
Mark = Lines,
Channel = Shape, Position Color
Tasks = Spatial Relationship

Question 7

Caution with Maps (V1)

Answer 7

A dataset may contain geographical information
* Yet creating a geographical visualization may not be
relevant.
* Ask: “does spatial arrangement matter for my task?”
* Position most effective visual channel  do not waste
it, if not relevant.

Absolute vs Relative

Question 8

Network (V2)

Answer 8

Describe the relationship between objects
represented as tuples of verticies and edges
- Undirected OR Directed

Question 9

Tree (V2)

Answer 9

Special type of network that has hierachy
- a graph without cycles (acyclic) and has one root
- nodes have 0 or more children

Question 10

Types of Static Networks (Design) (V2)

Answer 10

Types (Design choices for arrangement):
1. Node-link diagram (both)
2. Adjacency Matrix (both)
3. Enclosure (does not represent network, only tree)

Structure is important, shows areas of interest

Question 11

Types of Network Structure (V2)

Answer 11

1. Radial
   - hides a lot of info, structure depends on ordering of nodes
2. Arc
   - edges move clockwise. top are left to right, bottom right to left
   - linearise nodes! (sort/ordering)

Question 12

Layout/Embedding (V2)

Answer 12

Positioning of nodes

Question 13

Things to do when Visualising a Static Network (V2)

Answer 13

1. Maximise Readability & aesthetics
   * Equal edge length
   * Minimize crossings
   * Non-overlapping nodes
   * High-degree nodes should have a central position
   * Symmetry should be maximized
   * Communities should be clearly visible
2. Optimise structure using node force directed algorithms

Question 14

Issues caused by Large Networks, Solution? (V3)

Answer 14

Methods used to visualise static network do not apply, as there is too much data -> hairball visualisation

Use other attributes from data such as Hierachy (from data OR computed) and node+edges Force directed algorithms to give structure

Question 15

Visual Adjacency Matrix for Large Networks (V3)

Answer 15

1. More scalable compared to node link diagram
   Use color (transparency) to denote weight of edges
2. Maximise edge visibility

*no crossings, cannot find paths easily
*ordering of nodes is important

Question 16

How to get good ordering for Visual Adjacency Matrix, for Large Networks (V3)

Answer 16

Additional Hierachal Data (from data OR computed) (hieracheral clustering)

Question 17

Which (design) choice of networks is used for Trees? (V4)

Answer 17

1. Node Link diagram
2. Enclosure
   (can combine both methods into one visualisation)

adjacency matrix is hardly used due to the structure of the tree, data will be very sparse

Question 18

Nodelink Diagrams for Trees (V4)

Answer 18

standard node-link diagram wastes a lot of space, instead use radial layout (root node in middle)

if tree is very big, use hyperbolic technique

Question 19

Enclosure Diagrams for Trees (V4)

Answer 19

1. Venn Diagram,
2. Treemap
3. Nested Treemap

Question 20

Treemap VS Nodelink (V4)

Answer 20

Treemap:
+ scalability is milions of items, better then node link. limit is screen resolution
+ Good usage of Space
- Hierachy/order is implicit (not shown directly)

Node-link
+ intuitive
+ good at exposing structure of information
- empty space

Question 21

Treemap Space Filling Techniques (V4)

Answer 21

Slice and Dice Layout:
* leads to very long/elongated rectangles (due to switching between vertical and horizontal cuts),
use Squarified Layout instead:
* however, comparison between dynamic hierachy is impossible

Question 22

Dynamic Networks (V5)

Answer 22

Networks that change over time
- edge is represented by vertices AND time-stampP

Question 23

Properties of Dynamic Networks (V5)

Answer 23

Structural Properties:
- communities
- motifs

Temporal Properties:
- Trends
- Anomalies
- Periodicity
- Temporal Shifts

Question 24

Understanding Dynamic Networks (V5)

Answer 24

Discovering/Exploring states
* Characterizing the evolution of
the network
* Stable states, recurring states,
outlier states
* Transitions between them

Question 25

Methods to visualise Dynamic Networks (V5)

Answer 25

1. Animation (mapping time to time) 2. Small Multiples (mapping time in intervals) 3. Integrated approach (mapping time to space)

Question 26

Animation to Dynamic Networks (V5)

Answer 26

for each time stamp, compute layout -> show changes + easy to implement + easy to spot big changes + applicable to all methods that a time stamp can be visualised - need to focus on many moving items simultaneously - keep track of multiple changes over time (relying on user memory) - change blindess (cannot see small changes) use: - preservation of the mental map (keep variation between layouts as small as possible) - add timeline control

Question 27

Small Multiples to Dynamic Networks (V5)

Answer 27

Juxtaposed visualisation using filmstrip or a grid layout + Can be used for any dynamic network - Decide on number of multiples used (too many = hard to spot changes, too little = can't see change)

Question 28

Integrated Approach (Mapping time to space) to Dynamic Networks (V5)

Answer 28

Provide static overview of entire time span of network in one visualisation + Complete overview + Global patterns are easily identified - Specialised Visual encoding, difficult to interpret for non experts - Restricted to specialised type of network

Question 29

Examples of Integrated Approach (Mapping time to space) (V5)

Answer 29

Clusters over time (Individual nodes and edges not visible anymore) Massive Sequence View (ordering is important) Parallel Edge Splatting (needs interaction)

Question 30

Idioms for Time-Series Data

Answer 30

Line Chart, Streamgraph Connected Scatterplot: same as normal scatterplot, but have multiple points connected using directed lines to show temporal ordering Gantt Chart: Data = 1 Categorical Attribute (Key), 2 Quantitative Attributes Mark = Line Channel = Horizontal position (start position), Length (duration) Tasks = Temporal Overlaps, dependencies between categories