Being conditioned by New York subway maps, I have to admit the London
schematic
map drives me nuts. I can't get a true sense of direction of how close a
station is to a landmark. Which leads to my next question ... do any
geographic
maps of the tube exist? Where are they?

There are some around but I can't say I've ever felt a need for them as the
stations are marked on street and bus maps and sooner or later one of those
will be required unless you are being met, in which case it isn't a problem.

The Jubilee Line goes to North Greenwich which is slightly off the beaten
track a bit. Unless that is where your friend has suggested you go to I
would suggest you ask him/her which station is the most convenient.
'Maritime Greenwich' is served by Greenwich station which is on the DLR and
also an overground line and the latter are often more convenient.

It might, for example, be more convenient to change from the Piccadilly to
the District Line at Hammersmith or Barons Court (you just walk across an
island platform there which is handy with heavy luggage) and then go to
Cannon Street for a direct train to Greenwich.

G.