A smart piece of spy-work. Veins on an ivy leaf show the outline of the fort as seen looking west (Point of the leaf indicates north.)
Here is another of the methods by which I concealed the plans of the forts I made.
First of all, I would sketch the plan as shown in the picture above giving the strength and positions of the various guns as shown below:
A. Kaponiers with machine guns.
B. 15 cm. gun cupola.