The information on how to use the "Trench Maps as part of an Unknown Project Case File" appears in a number of different topics, so here I have assembled the basics so they are all in one location.
This particular entry is specific to the French Trench Maps. If you are looking for the basic information on how to use the more common British Trench Maps, as well as the earlier Belgian maps, see this topic:
Using the French Trench Maps was entirely different. Initially I just avoided researching cases that had "Concentration of Graves - Burial Returns" (COG-BR) with the numeric coordinates (i.e. 260 x 190) as it appeared too complex to figure out the system. Eventually it became critical to a few cases, so the matter had to be resolved. These are some of the topics on the GWF that introduced the concept:
- Jonchery-sur-Vesle British Cemetery - the problem begins
- Help with Finding a 1918 French Map Reference near Dormans - the request for help
- Hermonville Military Cemetery - the map coordinates resolved
- Jonchery-sur-Vesle British Cemetery: Case #3 - Lieutenant Aviator at Courthiézy - the solution used in the first case
To start with, here is a sample of a CWGC Concentration Report (COG-BR) as it appeared in the first case at the Jonchery-sur-Vesle British Cemetery. The last entry on that page indicated that there was an "Unknown Lieutenant Aviator" in Plot 1 Row C Grave 4 and that the remains had been recovered at the location recorded as:
259.0 x 198.9
The first part was logical, there had to be a trench map in the 1/20,000 scale for the area known as DORMANS. It certainly was outside the scope (area) of the maps on the McMaster Lloyd Reeds Collection, so where was it?
Google maps helped us locate the area where the trench map covered, between Paris and Reims.
The community of Courthiézy was well outside the area of the Western Front where most of the Canadian Unknown Projects focused, generally north of the Amiens to Saint-Quentin line and the River Somme. The burial return did tell us that both Army and Airforce men were in this area. The initial cemetery investigated was the Jonchery-Sur-Vesle British Cemetery located in the Marne sector of France, the area first exposed to British troops in the Retreat From Mons in 1914 and then in the final phases of the Great War in 1918. Of the 101 known, of more than 350 burials, all are from the period after 15 May 1918.
Thanks to the assistance of Alain Dubois-Choulik, my "French Connection", we were steered to the collection of French Trench Maps:
Perhaps an easier site to use if your command of the French language is better than mine, but with some residual High School French and the assistance of Google Translate, the investigation could continue. The next step was to figure out how to use these maps, which were in Adobe Flash Format. Note that Flash Technology is on the way out (ends December 2020). Here is the process as described in the post using the Google Chrome browser:
When you get to the map page, and your French is 50 year old high school french, right click on the page and select "translate"
NB: follow the instructions on this page to enable the use of Adobe Flash in Google Chrome:
On the page that we opened in first step, click on the "Access the site" in the blue box on the right side of the page. If you want to stay in "english" then you probably have to click on the translate button on each page you open. You are now here:
Click on the image of the map where it says "1 picture" at the bottom. That will take you to the map page where you can change the size and all other wonderful things. You may be asked to click somewhere on the page to enable Flash or you may get a box that asks you to allow the browser to use Flash.
The information about the errors was in a post on a different topic (Hermonville Military Cemetery), so I have copied these over to this blog entry to continue with the project.
Here the investigation centered around the Lieutenant of the Northumberland Fusiliers in Grave 3.E.4 (COG-BR 2011835) who was found at trench map coordinates given as Berry-au-Bac 214 x 283, as were all entries on this page. The Lieutenant is the 4th entry on the COG-BR document.
Note that the location of the cemetery is Berry-au-Bac 222.5 x 289.5. We know from the CWGC information for the Hermonville Military Cemetery, it is located at GPS = 49.34061 x 3.9084 (49°20'26.2"N 3°54'30.5"E).
At present I do not know of any program to convert from French Trench Map Coordinates to GPS coordinates.
You can use the search engine on the site to find the map you want. In this case I just searched for Berry-au-Bac and then scrolled through the list. I see all kinds of photographs as well, so this is going to be rewarding!
Search Page:https://francearchives.fr/fr/search?q= (just type in "Berry-au-Bac" in the search bar and a list appears)
Results Page: https://francearchives.fr/fr/location/18328322 (I took the full 27 documents on the list)
The Map: https://francearchives.fr/fr/facomponent/92312a07d73a3e0c09e4ec5eee3326cf6e409e69
The Access Page for the Map: https://archives.marne.fr/ark:/86869/a0113584280865vxqZO
- The Map Appears Cote: 31 Fi 190: https://archives.marne.fr/ark:/86869/a0113584280865vxqZO/1/1 (when you click on the image)
- this is a 1/20000 map with X 212 to 226 and Y 287 to 308
- The Access Page for the Map: https://archives.marne.fr/ark:/86869/a0113584280865vxqZO
- The Map: https://francearchives.fr/fr/facomponent/92312a07d73a3e0c09e4ec5eee3326cf6e409e69
- Results Page: https://francearchives.fr/fr/location/18328322 (I took the full 27 documents on the list)
Check back at the SEARCH results and there are some other maps under the title of "Berry-au-Bac" that cover different areas
this one on page 3 (Cote : 31 Fi 121) of the search results is labelled Berry-au-Bac and shows GUYENCOURT (X=217.1 Y=291.5) in the middle of the page but not Berry-au-Bac
- Cote: 31 Fi 121: https://archives.marne.fr/ark:/86869/a011358428086VM2qxP/1/1
- the "X" axis appears to go from 213 to 220 and the "Y" axis from 287 to 298
- that means we can find the "X" axis at 214 but we are too far north to get a "Y" axis at 283
there are two more on page 2 of the search results:
Cote : 31 Fi 46: https://archives.marne.fr/ark:/86869/a0113584280850DZuCZ/1/1
- X 213 to 226 and Y 287 to 308 along with BLOCK LETTERS but not the same as the McMaster Map letters
- GUYENCOURT appears in the lower left on this map but it does appear at the same coordinates of X=217.1 Y=291.5
- obviously the map is a different scale - correct the one above 31 Fi 121 is 1/10000 and this one is 1/20000
- still too far north to pick up the spot where the remains were recovered
Cote : 31 Fi 191: https://archives.marne.fr/ark:/86869/a011358428086Cw7Gnt/1/1
- this is another version of the 1/20000 but for 24 October 1917
- looks like I have to find another map further south or a 1/50000
- Cote : 31 Fi 46: https://archives.marne.fr/ark:/86869/a0113584280850DZuCZ/1/1
There is no question now that the map references for the Northumberland Fusilier Second Lieutenant in Grave 3.E.4 is incorrect. The numerical coordinates may be correct but the map reference is incorrect. I found this by logging all the corners of the main 1/20000 map sectors. The lines run on an angle, slanting slightly from right to left from top to bottom, so the grids are not all exact. The red numbers refer to the vertical grid lines and the blue to the horizontal grid lines.
(see COMMENT #2 that contains and expanded level of detail for numerous maps in the Reims sector)
The top line of the COG-BR clearly says Berry-au-Bac 214 x 283 but that is impossible because those coordinates fall within the map for Jonchery-sur-Vesle. Of course, this in not the first time that the GRU, or whomever, has used the wrong map reference.
This error not only refers to this COG-BR document but to others in the series and perhaps others in the cemetery. For the grid references to be correct for any Berry-au-Bac entry, the first number must be greater than 211 and the second number greater than 287.
There are obviously cases where the numbers are reversed, which is depicted in the next example below.
On COG-BR 2011818 we see a set of coordinates for Berry-au-Bac 222.5 x 289.5 for graves 1.D.1 to 1.D.9. These then change to Berry-au-Bac 288 x 219, which does not fit into any of the maps. The numbers are reversed for graves 1.E.1 to 1.E.6. They do have the correct map, as the corrected first number is greater than 287. The error is continued on the next six (6) COG-BR documents and then at COG-BR 2011825 it reverts back to the correct numbering sequence but the wrong map reference - those stated as Berry-au-Bac 220 x 285 are Jonchery-sur-Vesle 220 x 285. . The error starts again at COG-BR 2011828 and corrects itself at COG-BR 2011833.
Starting to learn how to use the French maps was most certainly complicated by the errors in the recordings! The only solution is IGNORE what name it gives for the map and put the numbers in the correct sequence, then find it on a map.
Applying what has been learnt so far took us to the next step in the process. In this particular case I was looking at whether it was possible to separate two Second Lieutenants of the Northumberland Fusiliers (this topic). All that I am discussing in this blog entry is the use of the trench maps, which was just starting to develop during that case investigation. The two Second Lieutenants were the ones on COG-BR 2011835 (detailed above) and the other on COG-BR 2013869.
You will see on the main index page that we are in the area around REIMS and there are 1/20000 maps for Chemin-des Dames, Berry-au-Bac, Jonchery-sur-Vesle and Reims (just as examples). When you get into the smaller sector maps, remember that these are French so they are not NW, NE.SW.SE but NO, NE, SO, SW (West =Oeust). Yes, I felt like a dummy when I realized that!
Note the small green square at the bottom of the page tells you where you are:
Now we go look for the Jonchery-sur-Vesle map, following these steps and the instructions: (from the Main Map Groups for the Marne)
1/20000 Marne maps: https://francearchives.fr/fr/facomponent/9387ee39e8bf8a6d0ee835731e93b0b9aab36521
From list clicked on Jonchery-sur-Vesle: https://francearchives.fr/fr/facomponent/29207c548ae3e1ec74ee45cb0f5d95662329b101
Caution: click on the words in Blue Box on right of page "Acceder au site", not on the map image (only a thumbnail)
Now you can click on the map image and that opens the map (DO NOT use RIGHT CLICK to open in a new tab - does not work)
Opens in a new window:
- Now you can click on the map image and that opens the map (DO NOT use RIGHT CLICK to open in a new tab - does not work)
- Caution: click on the words in Blue Box on right of page "Acceder au site", not on the map image (only a thumbnail)
- From list clicked on Jonchery-sur-Vesle: https://francearchives.fr/fr/facomponent/29207c548ae3e1ec74ee45cb0f5d95662329b101
The next one in the Hermonville British Cemetery was not found at Berry-au-Bac 214 x 283 but at Jonchery-sur-Vesle 214 x 283.
Once both of the errors are corrected, it is clear that the two Northumberland Fusilier Second Lieutenants were recovered about 2,000 metres apart.
This is the map from the post above to which I have added the other 2nd Lt in blue. Yes, the numbers are for the blue one are also reversed to show X and Y and not as in the red which was Y and X.
It is quite possible that the GRU staff who were conducting these investigations in 1919 were dealing with the same issues we are discussing in this blog entry - how to use the French trench maps! It is important that we have identified the errors and now know what steps to take to make the corrections.
With this information in hand, we can now continue to investigate these cases. The first one where we will be using this information to submit a case file to the CWGC is:
If you have any questions about this topic, or have noticed errors that I have made or perpetuated, please do not hesitate to let me know. You can add a comment at the end of this blog entry or send me a PM.