The map M-1928 door is reserved for officers to put their operation cards, pens, plans,... all of this to be at hand, it could not be carried in the regulatory bag and therefore had to be created a special card door. The Interior consists therefore slots for pencils and pens for the rule... and also an envelope in acetate, a pastque to protect the cards. He was with a strap with shoulder reinforcements, that is sticking to the two straps at the top of the bag.
Here are the photos of this door cards: