Ben Nunn:
Indeed, as South Acton closed about 1959.

Yes, that's the earliest of the changes Charles mentioned, and it has
to be before that.

If the map has White City on the Central Line (as opposed to Wood Lane) then
it's post-1947. If Tooting Bec is no longer called Trinity Road, then it's
post-1950.

There were two significant service changes in the late 1950s that might
have been reflected on the map, but they weren't, so they doesn't help.
The Epping-Ongar service changed from BR steam trains to electric tube
trains -- but still without running trains through Epping -- in 1957, and
the Aldwych branch changed from full-time to rush-hour service in 1958.
But I'm looking at some 1950s maps in Garland's book right now, and as
I said, these changes aren't shown at all. The "rush hour" annotation
appeared on the map sometime later.

I'm curious whether this monochrome version is laid out the same as the
full-color version of that period. I would expect so, but let's see.

* Most lines are horizontal or vertical; the only diagonal sections are
the Central Line's West Ruislip branch, the Bakerloo south of Baker
Street, the Waterloo & City, and two sections of the Piccadilly.

* At the points where a line is shown as changing direction, it is
drawn as curved, except in some of the places (e.g. Rayners Lane,
Acton Town, Baker Street) where there is also an interchange there.

* Except for the Circle Line, where two lines share track -- e.g. the
branches to Uxbridge, Hounslow West, and Barking -- they are drawn
as if two separate lines, with station symbols on both, but only one
station name for the pair.

* Triple-circle interchange symbols are used at the following stations.
Laid out horizontally: Waterloo. In a triangle: Charing Cross, Holborn.
Vertical: Hammersmith, King's Cross St. Pancras, Mile End. Diagonal:
Moorgate. Vertical/diagonal combination: Paddington, Bank, Whitechapel.
(Charing Cross, of course, is the station now called Embankment.)

* 2 southern, 3 western, and 6 of the northern termini are all aligned
near the respective edges of the map, and the other 3 northern termini
(Stanmore, Edgware, Mill Hill East) are drawn aligned with each other.

Is that what it's like?
--
Mark Brader | "Do I look stupid?"
Toronto | "Yes, actually, a little. It's one of your
| greatest professional assets."
| -- Spider Robinson, "Lady Slings the Booze"

My text in this article is in the public domain.