SR2020 "Complexes" are the "hubs" of each improved hex. Any hex that contains any type of facility besides the natural cities/towns and villages must have an artificial complex/hub at its center. Settlements such as villages, towns and cities are themselves supply-generating hubs around which many facilities can be constructed. Barracks, air fields and sea piers can be constructed with non-military settlements as their hubs, but military fabrication plants and fortifications cannot.
Each "hub" provides some supply and serves as the central structural/supply point for further surrounding upgrades or "nodes" such as military bases, fortifications, plants, mines, oil and power facilities and all other commercial/civilian structures.
All Complexes/Hubs generate a certain amount of supplies to nourish its surrounding facilities/nodes. Once a "hub" Complex is constructed, up to six "node" facilities can be constructed in a "wheel" around it, in the same hex.
Since every non-complex facility is attached to a central complex in SR2020, no "node" facility can be rendered totally without some level of supply since all such node/facilities are attached to a supply-generating complex or city.