That is very interesting. I wish there was a more complete legend though. There are three types of lines that look like railroads to me, solid coloured for the trenches and dashed outlines for tunnels (I assume), although the roads are clearly solid outline so maybe dashed outline is ... foot paths? No, maybe filled in trenches? Covered trenches? The lines of x's must be barbed wire.
There is a place there they named "Machine Gun Farm".
Edit: I figured out two of the symbols for rails, the single line and double line, because that is pretty obvious, but the one with outline and solid dashes in it I still don't understand.