Graphics Reference
In-Depth Information
Chapter 1
Why Graphs?
This topic is about graphs and how graphs can be used to help solve business
problems. When many people hear the word “graph,” they think bar charts
or line charts, and rightly so, because those are also sometimes known as bar
graphs or line graphs. This topic is not about charts. This topic is about the
node-link diagram kind of graph.
Atitsessence,a
graph
isastructuredrepresentationofconnectedthingsand
how they are related. As you will discover in the following chapters, graphs
are capable of representing complex data in a way that an analyst can make
sense of.
Because graphs have a long history in mathematics, discussions about graph
analysis and visualization tend to include a lot of confusing esoteric terms
such as
edge
and
degree
. This area of study responsible for this is generally
known as
graph theory
.
For the discussions in this topic, we use more universally accessible and
less ambiguous terms where possible. For example, a
link
is a relationship
between
nodes
and is typically drawn as a line. Nodes are entities (or
essentially “things”) that are joined by links. Nodes are often represented
visually by a circle.
An edge is another word for a link in graph theory, and the term
degree
becomes a little less opaque if you are familiar with the concept of
six
degrees of separation
, popularized by the play and movie of the same
name. But only a
little
less opaque, because not only can “degree” mean the
minimum number of steps of separation between linked entities, it can also
mean the number of link connections that a node has.
Note
The glossary at the end of this topic can serve as a cheat sheet if you find
you need a little graph-theory-to-English translation.
In some circles, graphs are still viewed as abstract and
difficult-to-understand constructs used mainly by scientists walking around
