Convention in the past was always "up" to the larger city or
Capital.
Although "north" does seem to be more up than south.

That's right, one went 'up to London' regardless of the
starting point.

I wonder if that is from a London vantage point, because round
here no one would think of saying they were going up to
London.
From the SW I think they do

I gather it was from a railway operations point. They defined
the 'up' line as the one going towards London and the 'down'
line as the one going away from London. So yes, it's a very
London-centric view of the world.

Of course it breaks down completely when you have to discuss
journeys which don't include London, especially between two
places which are closer to one another that either is to London,
like Edinburgh and Glasgow or York and Manchester.

As far as I'm concerned I go 'down' to anywhere south, 'up' to
anywhere north, and 'over' to somewhere which is neither north
nor south.

Anne