MIG wrote
[...]
Geographically north of the river indeed. Rivers are geographical.
I
have no problem with that.

If you look carefully at the boundary between Surrey and Middlesex (now
between Elmbridge or Runnymede and Spelthorne) you will see the
boundary is not the river Thames but where the river Thames used to be.
So it's "recent", but more geologically "recent" than geographically
so.

--
Mike D