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# Chapter 1Why Graphs?

This book 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 book is not about charts. This book is about the node-link diagram kind of graph.

At its essence, a graph is a structured representation of connected things and 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 book, 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 ...

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