The different mechanisms that may influence the probability of a connection between two nodes.

In each of the instances, the distance from node A to B and from node C to B are equal. In figure (a) the link probabilities are determined by the combined radii of the nodes. It is much more likely that nodes B and C will form a link due to their radii. In figure (b), the probably of a link between nodes A and B increases because node A is a hub (i.e. high node degree), even though it still has a small spatial reach. In figure (c), nodes A and B have a high probability of forming a link because they are both in the same community. In contrast the probability of a connection between B and C is reduced because they are in different communities.