Page:Graphic methods for presenting facts (1914).djvu/269



24. Very large size celluloid-covered tack.

It will be seen from the foregoing list that the possibilities for ingenuity in map and pin presentations are almost unlimited. The celluloid-covered tacks having large flat heads, shown in Nos. 18 to 24 inclusive, are not as generally used as they might be for map work. Map pins and tacks of this sort placed upon the surface of a map can give a spot map with any desired diameter of spots, no matter what size of map is used or what the amount of photographic reduction may be. It is simply a question of selecting from the spherical heads, 8 or 10, and the flat heads 18, 22, and 24, to determine which size head is best suited to the size of the original map and to the size of dot desired in the finished illustration. Large celluloid-covered tacks 18, 22, and 24 are also valuable to show the location of main offices and different factories, or the locations of particularly important distributing points. The pins numbered 8, 10, 18, 22, or 24, are five different sizes of pins which may be used simultaneously on the same map to show different degrees of importance in the things represented.

When used for photographing to produce an illustration such as is shown in Fig. 196, lettered or numbered pins should have a black background so that the black circle outlining the tack head will show out in clear contrast against the map itself. This requires white figures on a black or red background. Pins having red letters on a black background cannot be used for photographing, as the red letters would photograph black and disappear entirely, leaving a solid black circle instead of a circle with figures. Since pins with a black background and white figures are not commonly obtainable, it may occasionally be necessary to use pins like No. 20 in Fig. 199 having black figures on a white background. Sometimes it may be feasible to draw an ink-line circle around each number which appears in the photograph so that the circles will be on the copy sent to the engraver who makes the zinc plate.

When pins must be used to locate agencies, stores, or other things which are usually concentrated in cities, the limitations are rigid because all pins should be located on the map immediately above the point representing the city. Crowded pins usually have to be spread horizontally over a wide area, and when so spread out it is impossible to tell which of several adjacent cities the various pins may represent. Fig. 200 depicts what was done in one case to get over this difficulty,