Accuracy of WW2 military topographical maps

[Rokko]

Hi folks,

For my Caen Area mega map I've been comparing the contour lines of some of the historical maps posted in the 12th SS campaign thread with the data I've used which is essentially from Google Earth and modern day maps by IGN and I've come across some pretty severe differences. The general heights are the same of course, but where the contour lines is pretty different. For instance the historical map has a 80m contour line marked as objective for an entire batallion, where according to the modern maps there is nothin the like there.

So could it be that things have changed that much in the last 70 years or are the military maps from 1944 just inaccurate?

I believe I've once heard that the US Army maps of the Hurtgen Forrest were very inaccurate and didn't have all the deep valleys marked, which supposedly caused great problems during the fighting there, so maybe that's a likely option than great changes in the landscape in less than a century

[Broadsword56]

To be sure, some postwar changes to elevations/topography will have happened -- particularly in places that have seen a lot of development.

But for the most part, I'd trust Google Earth and/or modern topo maps more than WWII era ones for elevations (and only for elevations). The technology is more precise now, and I think a lot of the WWII maps were rushed out and often based on old and imperfect prewar maps anyway.

For anything other than elevations (building locations, roads, vegetation, etc) I trust WWII or late 1940s aerial photography most, followed by official maps.

Best of all is a multiple-source approach: Make a Gimp or Photoshop reference image with each of your layers superimposed in place on it (elevation contours, aerial photo, troop positions, etc.) Then you can show or hide whichever layer you need at the moment, size it for your overlay, and place it in the CM editor.

[winkelried]

Agree with you Broadsword. One always needs to assess the amount of change that has happened since WWII on modern maps (including, but not restricted to elevation - creeks, trees, hedges etc are also subject to a lot of change).

I am a bit careful with google earth/maps data. Sometimes i am not sure what the base data is (especially for elevation) and how well it is aligned and fits reality. I found some strange anomalies with google earth data in my work.

what i usually do is to create several overlays:

- aerial photograps (mostly contemporary - 1940s)

- maps of the era (anything above 1:25'000 is pretty useless) or older.

- modern maps.

- sketches made by locals.

and (if possible) i make personal visits to the area to get a feeling of how things look - e.g. if creeks are an obstacle just to vehicles or not.

[winkelried]

ah forgot one thing:

instead or to prepare personal visits i use google streetview quite a bit (where available).

[Rokko]

Thanks guys,

Thats how I figured things went as well, I just couldn`t explain the inaccuracy of the Canadian maps. But I made an overlay in GE with an IGN map overlay and GE contour lines lined up pretty well with the map contour lines although the map was more accurate of course