Network analysis glossary
Brokers, bridges and structural holes
A broker is a person who links people or groups that would otherwise be apart. The gap they span is a structural hole. When removing one person would actually split the network in two, that person is a cut point, or articulation point, and the network depends on them entirely.
Updated · Netgraf
| Person | Removing them splits the map |
|---|---|
| Guadagni | Yes |
| Medici | Yes |
| Albizzi | Yes |
| Salviati | Yes |
4 people are a cut point on this map. Computed live from the example map with the same code the Netgraf insights panel runs.
Structural holes and weak ties
Ronald Burt's theory of structural holes (1992) argues that people who bridge disconnected groups get earlier, more varied information and can play the groups against each other, which is why brokers are paid, promoted and listened to out of proportion to their number of ties. It builds on Mark Granovetter's "strength of weak ties" (1973): new jobs and ideas tend to arrive through acquaintances, because close friends already know what you know.
Cut points
Betweenness centrality measures how much of the traffic a person carries. A cut point is the stronger condition: there is no other route at all. Remove a cut point and some people can no longer reach others. Hopcroft and Tarjan's 1973 algorithm finds every cut point in one pass over the network.
In the Florentine families the Medici are a cut point: some families reach the rest of the elite only through a Medici marriage. That dependence, not their wealth, is the structural story of their rise.
In Netgraf
Size the map by Holding it together (betweenness) to see the brokers, and check the Insights panel's How it breaks up card for islands and people with no ties. The worked example below lists this map's cut points, computed live.