In many cases solder is unnecessary, for the strips may be held vertically by notching each strip halfway through so that the strips can be interlocked in the manner shown in Fig. 236. By using sheet metal a much cheaper construction can be obtained than by wood strips. The sheet-metal method also permits the use of a map of much smaller size and finer scale than would be feasible if wood strips were the means of obtaining the necessary vertical height.

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Chapteb XII MAPS AND PINS

PIN MAPS have not been much used in the past, chiefly because a map pin which would give satisfactory service has not been available for common use. Until recently the map markers obtainable have been little more than old-fashioned carpet tacks having chisel-shaped points which cut the surface of any map into which they were pushed. Tacks with rough steel shanks cannot be pushed far into a map if the tacks are to be pulled out again. Also, rough steel is likely to rust so as to cause the whole tack to deteriorate rapidly.

Cloth heads on the map tacks make it possible to have tacks in distinct colors and plaids. The cloth tops, however, fade in the sunlight and collect dust so that in a short time the different colors of tacks on any map, exposed as a wall map must be, cannot be easily distinguished. The crudeness of the cloth-covered tack makes it unsatisfactory for many kinds of map work. Cloth-covered tacks are long, and long tacks which can be pushed only a short distance into the surface of a map are not satisfactory, for they are likely to drop out or be knocked off by any slight disturbance.