I went to play my first game of Halo Action Clix and after unfolding the map, the thing folded back up because it had been stored in that state for so long. So I set out to find a way to solve the problem and this is what I came up with.
The first thing I should say is that this process will make the rules on the opposite side of the map unusable, so be sure you have another copy lying around somewhere.
Begin by cutting off the non-map portion of the sheet. Its not necessary to have loads of Halo Action Clix advertising around the board.
You will need the map, some poster board, rubber cement, and masking tape.
Start by cutting the 10x10 map into four 5x5 squares. You should now have four quadrants. One has numbers and letters on it. Another will just have letters. The third will only have numbers and the fourth will have neither.
Trace the outline of each quadrant onto the poster board and cut it out. So now you have four squares of poster board which are the same shape and size as the four map quadrants.
Now you want to make the maps be able to hinge so that they can fold up for storage. Apply two pieces of masking tape to the poster board joints as shown. Only three of the joints will be taped, so that the board can fold up as shown in the corner of the image. Be sure to apply tape to both sides of the poster board to make the hinges even stronger.
Its time to glue the map quadrants down to the poster board. I used rubber cement to glue the map quadrants back down. The quadrant with the numbers and letters will go in the upper left corner. The quadrant with just the letters will go in the upper right corner. The quadrant with only numbers will go in the lower left corner and the quadrant without either will go in the lower right corner. All the text on the maps should be readable if you are standing at the bottom of the map and looking towards the top.
Let the glue dry and this map will be ready to be used in Halo Action Clix Battles. You may need trim some extra poster board from around the edges. Also, you may want to consider making the black wall lines a different color to make them more visible.