Lecture 5: Visualization Principles III

Question 1

Describe a Scatterplot Matrix

features of SPLOM

Answer 1

N attributes
N² scatterplots
Every pairwise plot is shown twice
Symmetry along diagonal
Diagonal can be used
‣ for showing labels
‣ for showing histograms of attributes

Question 2

What are the limitations of Parallel Coordinates?

Axes represent attributes
Lines connecting axes represent items

Answer 2

Scalability to Many Attributes
Scalability to Many Items
Correlations Only Between Adjacent Axes
Ambiguity
Not very popular / difficult to interpret
Limited to quantitative attributes
Patterns depend on scales
Missing data

Question 3

Explain pros and cons of Radial Layouts

Answer 3

Pro: Visualizing cyclic patterns
Con: Distortion

Question 4

Describe a Heatmap

Answer 4

Maps attribute value to color
Matrix data: two keys, one value
‣ Example: gene expression dataset [key1: patient] x [key2: gene] value = activity of gene
‣ Each cell is a “pixel”, value encoded using color
Meaning derived from ordering
‣ Order by time, frequency, etc.
‣ If no ordering inherent, clustering is used
Strengths
‣ Scales to large matrices
‣ Good for homogeneous data
‣ All columns share same semantics

Question 5

What is the Königsberg Bridge Problem?

Answer 5

Find a walk through the city that crosses each bridge once and only once
Negative resolution by Leonhard Euler in 1736
Laid the foundations of graph theory and prefigured the idea of topology

Question 6

What are some types of graphs?

Answer 6

A tree is a graph with no cycles
A directed graph (digraph) is a graph that discerns between the edges direction.
A hypergraph is a graph with edges connecting any number of vertices.

Question 7

What is a Adjacency Matrix suited for?

Answer 7

Well suited for neighborhood-related tasks
Not suited for path-related tasks

Question 8

What is the Mercator Projection?

Answer 8

Gerardus Mercator, 1569
Projection onto a cylinder wrapped around the globe
Conformal map projection —> angles are preserved
Pro: all lines of constant bearing are straight lines
‣ Constant compass heading for sailors

Question 9

Describe a Choropleth Map?

Answer 9

Greek: chore = area, pleth = value
Area uniformly colored/shaded proportional to attribute