Where does hub collide?

The central facility in a hub-and-spoke transport or distribution network, through which flows between many origins and destinations are consolidated and re-routed rather than sent directly: concentrating traffic at a few hubs lets an airline or carrier serve many city pairs with fewer links and fuller, cheaper vehicle loads. O'Kelly's 1987 A quadratic integer program for the location of interacting hub facilities set out the problem of where to place such hubs so that the total interacting flow cost is minimised. The referent is a chosen node in a logistics network, valued for the routing it enables, not a device on a wire, a well-connected point in an abstract graph, or the centre of a wheel.[1]

Unit

A consolidation node in a transport network, by routed flow and cost

Recovery means

Not applicable

Measured by

Assessed by throughput, connecting traffic, and the flow-weighted routing cost of the network it anchors

A node whose degree is far higher than that of a typical node, so that it connects to a disproportionate share of the network: in a scale-free network the degree distribution follows a power law, which makes such hubs both expected and structurally important for connectivity and for how failures or contagions spread. Barabási and Albert's 1999 Emergence of scaling in random networks showed how growth with preferential attachment produces this heavy-tailed distribution and the hubs in its tail. The referent is a property of a vertex in an abstract graph, fixed by its degree, not a transport facility, a repeater device, or a mechanical centre.[2]

Unit

A vertex of unusually high degree in a graph

Recovery means

Not applicable

Measured by

Identified by node degree or a centrality measure, and by the heavy tail of the degree distribution