A wall exhibit like this is easily made by using a red legal seal and red stars such as can be purchased at

many good stationery stores

way. A wall map on which pins with spherical glass heads are used can be very cheaply mounted, it needs no glass cover, and the pins can be put in or taken out instantly, thus giving a location record which is at all times in plain view, yet thoroughly accurate.

Another great advantage of the pins with spherical glass heads is that they may be obtained with small-diameter heads, which permit the use of numerous pins on maps of small size. In portraying many

230 GRAPHIC METHODS

classes of information, it is impracticable to use the cloth-head tacks because the heads are so large that the tacks touch each other in all thickly populated regions.

Photographs taken of a map containing tall pins or tacks give an inaccurate effect, since the angle of the lens causes the head of the tack to appear at one side of the point in which the tack itself is located. Thus, in a photograph of a map of the United States the head of a long pin or tack set at Providence, R. I., might well show near Boston, Mass. There is no way of avoiding this error if projecting pins and tacks are used. The only safe plan is to use the spherical pin head which is in contact with the map surface itself. Photographic views of a sphere are the same from all directions, thus causing all pins to appear exactly the same size and shape on the photograph. Photographs taken of a large map with flat-headed tacks show the heads in the center of the picture as circles, while the heads towards the edge of the picture look of much smaller size, because they appear flattened out as ellipses.