Displayed here is a map of Germany, printed on very thin silk, rayon or tissue paper.
They could be concealed in a packet of cigarettes or in the heel of a boot.
Two prison camp areas are circled, (BALE) and (HARRIS) details on this web site were held prisoner.
Other camps can be viewed on the German POW Map.
Details are explained on a site by DEBBIE HALL.

The items displayed on this page were memorialized in the British Map Library a few years ago. The maps were hidden within the game of "MONOPOLY". The game was created by John Waddington LTD; licensed from Parker Brothers, for the British Secret Service.

This author remembers tokens of 1935 well. Perhaps the inside of the top hat and thimble is where the most room was to stuff a small map. However the tokens used for passing maps were likely like those shown on the right, below. Probably molded around a map. Ten are shown here. Perhaps there were quite a few guys actually playing the game and many different tokens were needed. That pig, looks cool!
The images came from: MONOPOLY HISTORY.

The link above to "DEBBIE HALL" also tells about how prisoners made their own maps. See PRINT ROOM below.

Below that is a copy of letter used to order maps.