JP6004
My point is the gateshead borough is defined as one zone, travelling from outside of this zone, say from Chester or Washington would naturally cost more

But it's not defined as one zone as there are anomalies such as the ambiguous Newcastle/Gateshead bubble and the fact that Springwell Village is included despite not being in the borough of Gateshead.

You can make the same argument for Sunderland with the inclusion of Murton and Seaham, both if which lie outside the Borough of Sunderland.

Mark.