My investigation into the Space Allocation Problem also led me to learn about Graph Theory. Graphs are a discrete mathematical structure where nodes are connected by edges.
Graphs have a great number of applications, within architecture they can be used to diagrammatically describe the adjacencies between rooms within a house (Hillier, 1987).
House plan and genotype graph of Le Cormier (Hillier et al., 1987)
But they also have applications within many other fields. Online, for instance, Google recently implemented a knowledge graph alongside search results. If one searches for "Northumbria University" then Google presents all connected data for this place alongside the normal results.
LinkedIn, Facebook and other social networks are also implicit graphs, each person (node) is connected (edge) to friends or colleagues who in turn are connected to their friends or colleagues. Then through graph theory LinkedIn is able to determine the connections you may have to particular people.