do this class of work are not so easily found in the United States as in Germany.
An excellent map of this general type can be made by using sheet metal, as aluminum or zinc, ruled or painted with lines or colored stripes representing the vertical scale to which the information is to be shown. Where two transit lines intersect the strips of metal can be riveted or soldered together. As aluminum is not easily soldered it is best to use zinc or tinned iron if solder is to be the means of holding the vertical strips to each other. 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.
