I think Brigantia was bordered by rivers and the northern border was possibly the Tyne, that makes sense looking at the placement of Hadrians Wall. Not entirely sure though.

Perhaps we need to think of Thornborough as being a very large regional centre, surrounded by other, more minor works that by the end of the Iron Age had lost much of their relevance. Again local differences must apply.

We also need to bear in mind that we can only see about 10% of what the Romans did, and less of the prehistoric period, so our interpretation can only be a very flawed one.