Page:Graphic methods for presenting facts (1914).djvu/248

 Generally the tacks are placed in the maps one by one as agencies are established or as data are obtained from correspondence. After the correspondence by which each tack was located has gone to the correspondence files, there is ordinarily no list showing the geographical location of the tacks. If a single tack is found loose in the bottom of a drawer of a cabinet system, or on the floor of an office where there is a wall map, it causes distrust of the whole tack installation. When there is no list showing the geographical location of different tacks, the one tack which is out of place cannot be put back without checking over correspondence and records which may extend back for years. Even when a list of tack locations is at hand, the loose tack cannot be replaced without checking the location of all the tacks on the map one by one to determine by a process of elimination where the loose tack came from. In the ordinary course of human events it is not likely that a tack falling out of a map would be found to give warning that the map record is no longer accurate. The tack system using long projecting tacks may therefore contain unsuspected inaccuracies just because tacks may have come loose. The unpleasant suspicion that a map record may be inaccurate, because of the long tacks falling out, sometimes causes a man to abandon the tack system entirely, believing that it is not reliable enough to give data on which important decisions must be based.

Fig. 186. A Contrast Between Long, Cloth-covered Map Tacks which are Likely to Fall Out, and Glass-head Map Pins Made with Short Needle-points so that the Pins May be Pushed in until the Heads Touch the Map

Map and pin systems are of such tremendous assistance that they should not be condemned simply because the map pin itself has not been satisfactory. By using a short pin with a needle point and by having a backing for the map such that the needle point can be pushed in until the spherical head touches the map, we can secure a map system which is absolutely trustworthy. Since the pin is pushed in to its full length, a blow cannot dislodge it. The spherical head in contact with the map gives a very neat appearance, yet the spherical shape permits the fingers to remove the pin by straight pulling without any difficulty whatever. The smooth needle-point of good quality steel does not rust easily and it does not cut the surface of the map. When a pin must be removed, the hole is so small that it is scarcely noticeable.