Why is it called "up"?

[greg@mpx.com.au]

A few years ago I was at Chatswood station on Sydney's north shore,
waiting for a train to take me back into town. I poked my nose into
the old guards shed, and saw a bunch of levers and switches and stuff
that were marked "up", but it clearly referred to travel in the
southerly direction, towards the city and Central. 

I can see two things wrong with describing a train going from
Chatswood to Central as being "up":

1. From Chatswood to Central, you travel south, which on most sensible
maps is "down".
2. Chatswood is at about 100-150m altitude , while Central is pretty
close to sea level. Travelling from a higher place to a lower one is
usually described as being in the "down" direction.  

Why the confusing terminology?