Northern Heights on a Bartholemew map

Wow, thank you! Waiting for a pic impatiently

cool!
Another map-fan.
Is there any bit I should look to include to assist on dating?
(disclaimer, I do have a wedding, a racebike and lots of other tat to organise, so remind me if I forget).

The OS was a department of the military so there are plenty of wartime OS maps about only they were not available to Joe Public. I prefer to collect larger scale maps so I am not that familiar with Bartholemew maps but they were based on OS maps and published under licence from the OS. The OS maps have a revision date usually in a bottom corner and it would say something like this >>
Revised 1936.
Major roads revised 1937.
Selected revision 1939.
If you can find a copy of the OS map your map is derived from this will give you the information you require.
PS You will need a magnifying glass as the printing is minute.

No - the relationship between OS and the military is a subject in its own right, going way off topic - suffice it to say that the OS has been on its own since the nineteenth century, the military producing its own maps, although for the UK they are OS maps with military annotations

Whether non-military OS maps were produced during for official civil use I don't know, or whether such got 'military' maps I don't know


I would say that Barts maps were based on OS (survey) data (as are most maps of the UK), rather than any particular Barts map being based on some specific OS map - with the possibility of including other information from other sources. There's also a variation in the OS and Barts attitude to railways: OS have always regarded them as features on the ground, Barts seem at times to have regarded them as means of passenger transport, and ignored ones which aren't!
Another good dating aid is the magnetic variation date - but Barts did not always provide this.
The accurate dating of Barts maps can be non-trivial - I'm sure I've seen web pages on it.

Remember that the only bit of the Northern Heights extensions which was not built was Edgeware - Bushey Heath: everything else was built and existed as a railway (and so definitely on maps, OS or other). But both Barts and Geographers (A-Z) did put it on (some of) their maps - with or without an 'under construction' note: I have a Barts one-inch map somewhere with it, which I know I decided was a late '40s production.

Those photos are VERY interesting!!

For what it is worth, the 1950 AA Road Book shows the Watford bypass as A500.

When did the Wembley loop go out of use? IIRC it was pre war. As has been said it is very difficult to date maps by their features. The most frequent updates were carried out by the OS but as I stated only every 5-6 years at best and as Bartholemews and other publishers obtained their data from the OS it is probable that the period was extended and that there are several anomalies on the map. As it appears from what has been said there are some post war features on your map which will date it as about 1945-50. Don't forget that the green belt which effectively stopped the Northern line expansion did not come into effect until circa 1947 and many of these lines were still being operated by the main line companies.
Another significant feature that is missing is the Aldenham bus works, this was built before the war as the depot to serve the new lines. During the war it became a 'shadow' factory making bombers and for security reasons would not have been included but would have likely to have been on a prewar map.

Indeed - that is one of the interesting things about it. The LNER line did exist and ran to the LNER station in Edgware. Part of the Northern Heights Plan was to remodel it so it ran into Edgware LU (and thence onward). This is what fascinates me about this map - the extension is listed as fact, but the works that much more nearly did happen (IIRC one of the Edgware sidings is on the alignment), is not even marked as intended.

I remember a while ago some of the exhibition pavilions were going to be demolished due too the stadium re building. It is quite likely that a lot if not all of the remaining railway infrastructure has now gone.

Google Streetview shows South Way rising over the bridge across the former Wembley Stadium loop line.