You can read the following about the historical RB-map overlay:
Red Barricades Map Update Overlays
These overlays are based on data released after the original Red Barricades game was published. They are an attempt to make the RB geographic area even more accurate to its appearance during the battle. Use the hex coordinates printed on the overlays as a guide for their proper positioning. Players may, at their discretion, choose to use any or all of the below update overlays to alter the game map, but should keep in mind that such use may alter the balance or affect the VC of some scenarios or CGs.
RB Update Overlays - Cutting Instructions
These overlays should be cut exactly along the outer-most edge (i.e., where the full-color map art meets the white background).
Now, if you want to attach the overlays permanently onto the Red Barricades map and still have a RB map that is foldable and easy to store away in a ring binder or box. Then follow these Cutting Instructions.