Starships move from star system to star system by means of a "jump" drive, which drops the ship into jumpspace, an alternate dimension or state.
While there is a "geography" of jumpspace, it does not appear to correspond to the physical positions of stars, and in fact it is hypothesized that jumps don't violate causality because they cross into alternate universes.
Systems are mapped by the jump quanta between them, represented in a somewhat arbitrary two-dimensional "web." For instance, Pledger is two quanta from Wayoff, and only ships capable of jump-2 or higher may make the jump - "slower" ships must be ferried by larger, "faster" ones.
Similarly, Dhengdhoughz is 1q from Outsdurrgha, which is 1q from Uengrugz. A jump-1 ship can travel from Dhengdhoughz to Uengrugz, by exiting jumpspace at Outsdurrgha. A jump-2 ship does not need to exit jumpspace (though the intermediate system will figure into its navigation) for the same trip.
Quanta are not necessarily additive; Uengrugz is 1q from Outsdhurrgha, but is also 1q from Ughae. A jump-1 ship at Outsdurrgha could reach any of the other three systems in one hop; a jump-2 ship could also reach Ughae by Uengrugz, at a cost of spending longer in jumpspace. Multi-jump distances are qualified by ship capability - "twelve by two" means a jump-2 ship will make jumps totalling twelve quanta. The same two systems might be "fifteen by one" apart, since a "slower" ship might need a more circuitous route.