British First World War Trench Maps, 1915-1918

Sheet numbering and trench map references

Index of 1:20,000 trench map series
Index showing 1:20,000 trench maps on this website
View zoomable sheet index

Trench map sheet numbers and references are based on the Belgian 1:40,000 sheet lines, numbered from 1-72 to cover the whole territory of Belgium. As they were extended westwards into France, letter suffixes were added (eg. 36A, 36B, etc.) as shown in the index map to the right.

For more detailed scales, each 1:40,000 sheet was divided into four 1:20,000 sheets with NW, NE, SW and SE suffixes to the main 1:40,000 sheet number (eg. 36NW, 36NE, etc.).

Each 1:20,000 sheet was in turn divided into four 1:10,000 sheets with the numbers 1 to 4 as suffixes to the main 1:20,000 sheet number (eg. 36NW1, 36NW2, etc.).

Index showing relationship between 1:20,000 and 1:10,000 trench map sheet lines
The 1:40,000 Sheet 28 contains four 1:20,000 sheets
(28NW, 28NE, 28SW and 28SE - red) which each contain 4
1:10,000 sheets (eg. 28SE1, 28SE2, 28SE3, 28SE4 - blue)

Larger-scale sheets at 1:5,000 were not part of a standard series and were often given special names of their main location (eg. Eaucourt l'Abbaye ).

Trench map references use the main map sheet numbers described above, and divide the standard Belgian 1:40,000 sheet into 5,000 or 6,000 square yard capital letters, running from A to X. Each 5,000-6,000 square yard area was then divided into 1,000 square yard areas, numbered from 1-36, which were quartered into four 500 yard sub-squares, a-d.

For example, a reference such as Sheet 36NW,C23c7.4 gives first the 1:20,000 sheet number, then the 5000 yard square letter C, the 1,000 yard square number (23), the 500 yard sub-square letter c, the easting in tenths (7) and the northing in tenths (4). This locates a position just east of Armentieres

Although there was an earlier trench map grid system which subdivided each 1:40,000 sheet into regular 5,000 yard squares in 1914, it was quickly superseded and is not used on any of the maps on this website. The new system described above was sometimes marked “Revised system of squaring” on sheets.

Search using trench map coordinates

Screengrab of Explore Georeferenced Maps viewer showing Search Trench Map Coordinates search box

Our Map Finder - with Outlines and Explore Georeferenced Maps viewers allow you to Search Trench Map Coordinates in the search panel to the upper left. You can input various lengths of trench map coordinates (eg. '28.I.8', '36C.S.22.c', '62d.J.19.b.4.3') and the map will zoom to these locations. The longer your reference, the more accurate the location will be.

Screengrab of Explore Georeferenced Maps viewer showing the Trench Map Coordinates display

In our Map Finder - with Outlines and Explore Georeferenced Maps viewers, the Trench Map Coordinates for your mouse cursor location are shown to the lower right. If you click/tap on the 'Show Coordinates' tab in the footer, or hold the ALT button down and click/tap, these Trench Map Coordinates and the latitude / longitude coordinates of the place you have clicked/tapped on, appear in a popup box for copying.

We are very grateful to Bill Frost, developer of the tMapper website for sharing these trench map coordinate search and conversion utilities with us.

The tMapper website provides an easy conversion utility from trench map references to modern locations. It also includes a searchable gazetteer of trench names, and related resources and information.

'The Great War, 1914-1918' has an excellent guide explaining why the British Army required the Trench Maps at this scale, how the map reference system was devised and how to find a location using a trench map reference.

NLS collection

This website presents scanned images of all the maps held by NLS within the main two series of trench maps: GSGS 2742 (1:20,000) and GSGS 3062 (1:10,000), as well as NLS holdings of all larger-scale trench maps of the Western Front too. It should be stressed that the NLS collection is very incomplete, and much more comprehensive collections can be found within The National Archives and the Imperial War Museum.

This website includes:

These can be viewed as an ordered list by scale and date.

Identifying specific locations and battles