An interlocking network with cities at a nodal level, the network at inter-nodal level, and business service firms as a sub-nodal level. These last ‘interlock’ cities through their myriad networks of offices. In this new city system, it is the functions of a city that largely determine its role and importance nationally, regionally, and globally (Taylor et al. (2002) Urb. Studs 39, 13). See Beaverstock et al. (2000) Applied Geog. 20 on the conceptualization and measurement of the network connectivity of cities.