WWI Trench Maps & Aerial Photographs
Evolution of Mapping on the Western Front:
The following is a point-form outline of the evolution of British mapping during WWI based on the sources found on our "references" page.
It is hoped that it will help the map reader, when examining the maps in our collection, to understand more fully the information presented therein and to explain what appear to be inconsistencies, but are instead, differences resulting from the various stages of development.
Errors may be present in the sequencing of events within each year as minor discrepancies were found among the sources used to compile this chronology. It was also impossible to pinpoint the exact month in which each event occurred as evolutionary changes occur gradually and are not always adopted simultaneously and universally.

War Breaks Out (August)
War of movement ends after the Battle of the Marne. Both sides "Dig in".
Trench or siege warfare begins on the Aisne. Need for large scale maps becomes apparent.
Litho stones and plates for Belgian 1:20,000 & 1:40,000 scale maps and original drawings for 1:10,000s evacuated from Antwerp and shipped to British War Office in London (Ypres area well covered by these sheets).
French 1:80,000 series enlarged up to 1:40,000 and overprinted with squares for artillery purposes, but enlargement only results in accentuating inaccuracies.
Army Intelligence GS(I) originally responsible for mapping any territory forward of the front line but has no cartographic resources. Produces rough sketch maps at 1:5,000 and 1:10,000 scales called "Trench Diagrams" due to their lack of topographical accuracy (see example). Used in planning for first British attack after entrenchment at Neuve Chapelle.
British experiment with "B" series using their own grid lines in thousand-yard "artillery" squares on reproductions of Belgian maps which were created on metric sheet lines resulting in improper fit. Problems occur when plotting targets over 2 or more sheets (see example).
Maps are printed in England by the Ordnance Survey (O.S.) in Southampton and shipped overseas to the Front. War Office (W.O.) continues to print but only small scale maps.
New series of sheets of Belgium produced with sheet lines that fit the British artillery squares "A" series. This creates a uniform "theatre" grid which could potentially overlay entire area of operations.
British trenches, except for the front line, are not printed on maps in case they fall into enemy hands (see example).
"Revised System of Squaring" introduced for the Artillery which was identical for maps of all scales.
British Expeditionary Force (BEF) splits into 2 armies.

Maps General Head Quarters (GHQ) is established at St. Omer, France.
Mapping and Printing Sections are attached to each army. Equipment consists of hand-litho presses capable of printing 13" x 16" (foolscap) or 17 1/2" x 22 1/2" (demy) sheets. Most maps are still printed in England.
Plane table survey done of the area behind British lines.
"A" series inexplicably ceases.
Work on new 1:20,000 scale series (GSGS 2742) begins.
Belgian "Bonne" projection adopted as standard. French trig values converted to it.
Belgian survey lines extended to cover Northeastern France to create a common grid overlay.
Belgian map numbering system is extended to include new maps created for France.
Errors with "Bonne" projection and previous, hasty plane table survey result in re-triangulation.
3rd Army formed.
Three Topographic ("Topo") Sections created, one for each of the now three existing armies.
Printing Sections absorbed by Topo Sections.
New 1:20,000 scale maps are enlarged to produce a 1:10,000 series and reduced to produce a 1:40,000 series.
3rd Army produces new 1:10,000 "Provisional" series map using topo detail from French "War Plans Directeur" and trench detail from aerial photography (see example).
Flash spotting and sound ranging methods developed for pinpointing enemy artillery.
British adopt French ideas of bearing pickets and artillery boards.
Third Army produces first really good 1:10,000 scale maps (2nd Edition) by compiling a combination of French cadastral maps, plane table surveys by the 3rd Topo Section and aerial photographs.
1:10,000 series (GSGS 3062) adopted as standard base maps and 1:20,000s produced as photographic reproductions of them.
6th Edition of the regular series now shows identical detail, position and square referencing on 1:10,000, 1:20,000 and 1:40,000 series maps.

Three Topo Sections have grown and officially become three Field Survey Companies of the Royal Engineers (R.E.). Each has a separate section for surveying, map compilation, drawing, printing, and observation (which is made up of Flash Spotting and Sound Ranging groups formerly manned by Artillery officers).
2nd Army Topo Section revises and redraws Belgian 1:10,000s and drops unwanted conventional signs and 1 metre contour interval (see example). 5 metre interval is adopted as new standard.
4th and 5th Armies are created and Field Survey Companies added to each.
Aerial photographs begin to be taken in stereoscopic pairs.
Some British trenches are now allowed to be printed on maps but only the first 200 yards (see example).
Daily "Situation" maps created for the Battle of Arras (see an example of a "Situation" map).
"Positions" maps created in May by 3rd Field Survey Company and in July by 4th Field Survey Company in order to show all enemy battery positions located by aerial photography, flash spotting, sound ranging, kite/balloon, etc. (see an example of a "Positions" map).
Battle of the Somme results in creation of Artillery "Barrage" maps (1:10,000) covering 10 to 15 miles of Front with lines representing lifts of 100 to 200 yards every 4 minutes. Also, "Corps Front" maps (1:20,000) showing assumed identity of enemy units and their placement opposite Allied units. At this scale, the front of an entire corps can be shown on one sheet rather than two.
4th Field Survey Company allowed to contract civilian firms in Amiens, France to print base maps. Trench and Situation overprints still printed at HQ with hand-litho presses.
Some use of the "Vandyking" process begins in the field.

Depot Field Survey Company formed under GHQ in Montreuil, France for the purpose of training, research and equipment.
British trenches which can be discerned from aerial photography are now allowed to be printed on British maps. Only maps stamped "SECRET" show complete trench network. These are printed in very small numbers and usually not allowed outside of HQ.
Names for trenches on maps are adopted from soldiers in situ or created by the Field Survey Companies.
Entire British Front is now covered by 1:10,000 & 1:20,000 scale map sheets.
4th Field Survey Company experiments piecing together small glass plates in order to attempt heliozincography ("helio") process.
Corps Topo Sections created and equipped with duplicators to produce 12" x 16" (brief sheets) in several colours.
Field Survey Companies grow and are re-organized as Field Survey Battalions but not officially declared so.

Ordnance Survey, Overseas Branch (O.S., O.B.) established in Wardrecques, near St. Omer in France, due to threat to shipping as a result of German U-boat activity and possible German offensive after Russia drops out of the war. Printing of base maps in France begins.
All 5 armies now have "flat-bed" printing machines capable of printing 22 1/2" x 35" (double-demy) sheets.
German Offensive (March)
5th Field Survey Company retreats to Abbeville and its flash spotting and sound ranging groups are put into the line as infantry in the defense of Amiens. Heavy losses are taken.
3rd Field Survey Company keeps printing to the last possible minute before retreating from Albert resulting in the loss of a printing machine.
O.S., O.B. retreats to Wimereux.
Depot Field Survey Company performs urgent back area mapping.
"New Series" of 1:20,000 scale maps using French "Lambert" projection and grid for referencing begins development in order to correct discrepancies between Allied armies' trig systems and to take advantage of new French trig data for the Somme area. This requires recalculating all points onto the new projection.
Established practice of printing British trenches in blue and German in red is now reversed in order to create uniformity between French and British maps.
Field Survey Companies officially made into Field Survey Battalions.
Allied Offensive (August)
Success leads to rapid advances thus making the production of the large scale sheets no longer necessary. 1:10,000 series dropped after Battle of Amiens.
"Enemy Organisation" maps which combine trench and target detail are now the most common maps produced (see example).
War Ends (November)

Contact: mapref@mcmaster.ca