You're right Roldophe. The areas depicted on the SoW map look like they're lifted straight from modern day google earth.
Period orndance survey maps for the area can be found here:
http://www.ponies.me.uk/maps/osmap.html
If you compare the period map with the SoW offering you can clearly see how the individual settlements of the time have been merged and spread outwards. Canvey Island (highlighted in blue) did have a small development area but nothing like that presented on the SoW map (which matches modern google almost exactly).
Even more interesting is Basildon which in the 1940s was a collection of a few streets hardly worth mentioning. After the war this area was designated one of the modern "New Towns" and was massively expanded. This expansion is seen on the SoW map.
The sad thing is, if this is true, then the developers have spent hundreds of hours creating huge populated areas which never even existed at the time. I was really hoping to get an experience of flying over wartime Britain. It looks like what we'll be getting is a very modern Britain with all its huge, ugly post war expansion. A real disappointment for me.
With all the attention to detail the team has shown in the aircraft area, I really did expect to see at least a bit of basic research in the map department.
I do hope I'm proven wrong.