Researching WWI family history.

[Dianaa]

Currently I am reading the unit diaries of my grandfather's engineers unit in WWI. As part of this am trying to align fragments of oral history and events to entries in the diaries.

One problem I have come across is that many of the entries relate to grid square references on maps.

What I am wondering/presuming is that the maps were coded so that the grid numbering were only relevant for particular time periods and that at different dates during the war the same location would have different grid references. Is this correct?

Does anyone know if there is a source for British/Allied war maps, particularly for the period from the Kaiserschlacht around March 1918 through the Battle of Amiens to the Armistice in November 1918?

Diana