In the literature, the hub location problem is commonly modeled
as hub median or hub center problems (Meyer, Ernst, &
Krishnamoorthy, 2009). The main objective of hub median
problems is to minimize total transportation cost. If there is a
maximum limit on the number of hubs, it is called the p-hub
median problem. In hub center problems on the other hand, the
objective is to minimize maximum distance (cost) between
Origin–Destination (O/D) pairs. Next to these two formulations,
hub location problems are sometimes modeled as hub covering
problems where the objective function is to maximize the total
number of served spoke nodes. For an extensive study on hub
location problems, we refer to Alumur and Kara (2008).