I think in this case a hub is wherever the mainline partner has a central operation, i.e. LAX for DL/UA, SFO for UA, etc or there is a large percentage of aircraft movements. A domicile is wherever crews are based, so at SkyWest that includes outstations such as PSP, FAT and SBP. In the case of the 175s crews will be ORD domiciled to start but could fly a large portion of their trips through hubs elsewhere, LAX, SFO, DEN, IAH, etc.