This appendix will provide a very basic introduction to networks. This introduction is by no means comprehensive, but should be sufficient for those without network analysis experience to begin following the workflows in section 5 Sample Workflows. Networks, sometimes referred to as graphs, are comprised of two basic elements: points and lines. The points in a network represent entities and lines represent the relationship(s) that connect these points. The simple example below will illustrate this point:
These points and lines are often referred to by different terms. The table below should help you decipher any terms you encounter.
Throughout this manual we will refer to points as nodes and the lines as edges or arcs.*Arcs are directed edges, meaning that the relationship has a direction. You will see an example later in this introduction in the edge attribute section.
Some important node attributes include:
Betweeness Centraility - is the number of shortest paths a node sits between. In the case of the network below, Node A has the highest betweeness centraility because it sits between four edges that connect to other nodes.
Degree - is the number of edges that connect to a node. For example, Node A has a degree of four and Node F only has a degree of 2.
Isolates - are nodes that are not connected to any others through edges. In the network below Node G is an example of an isolate.
Some important edge attributes include:
Shortest paths - shortest distance between two nodes. For example the shortest path from Lenore to Mary is through Rupert and not through Chris and Jessica.
Weight - strength of the tie represented by the thickness of the edges between nodes. In the example below, the edge between Lenore and Chris is the strongest.
Directionality - is the connection one-way or two-way? In the example below, and in most directed networks, directionality is indicated by arrows.
In-degree - is calculated by determining the number of edges that point to a node, for example Chris has an in-degree of 3 and Rupert only has an in-degree of 1
Out-degree - is calculated by determining the number of edges that point away from a node, for example Chris has an out-degree of 1 and Rupert has an out-degree of 3.