Description: Sheet 20SW. Edn.4A. Area: north of Ypres - Yser from Loo - Zwartegat - Oostvleteren - Knockehoek - Steenstraat - Het Sas - Houthulst Forest - Bixschoote - Langemarck. Inundations in blue. German trenches in red; allied front trenches in blue. The situation just before the 3rd Battle of Ypres - northern part of battlefield. Ochre contours.
