WWI Trench Maps & Aerial Photographs
GSGS Number
The letters "GSGS" stand for "Geographical Section, General Staff" and the number following identifies a particular map series produced for the GSGS. These numbers can indicate map series of different scales or different purposes like "Enemy Organisation" or "Situation" maps.
The image below is taken from the bottom margin of a trench map.
GSGS number

Contact: mapref@mcmaster.ca