Photographs for line cuts must have a good contrast of white and black, or colors which photograph as black. Photographs or original drawings containing shades of gray will not produce good line cuts and frequently cannot be used at all for the zinc engraving process. When line cuts are to be made from pin maps it is best to be certain that the glass-head pins are selected in colors which will photograph as black. Red, orange, and black pins can be used without any question, since negatives made from these colors give a dead black on the photographic print. Line cuts can also be made from dark green and some of the other colors. Where it is necessary to make photographs and line cuts from a very expensive and elaborate pin map, it is wise to consult the engraver before the pin colors for the map are finally decided upon. The color blue should be carefully avoided if photographs or line cuts are to be made, since blue almost totally fails to show up on a photograph.
If half-tone engravings can be used to illustrate the pin map, many more different colors of pins may be used on the original map than when zinc cuts are the means of printing. Another advantage of half-tones is that different colors of pin heads are represented in the half-tone by different shades of gray, as can be seen in Fig. 191. On the left half of Fig. 191, fourteen different colors of glass-head map pins were used. The photograph was not retouched in any way. Fig. 191 thus represents about what can be expected of different colored pin heads for contrast in half-tone illustration. Note the high lights which give white spots on the circles of the darker pin heads. It is spots like these which should be retouched by hand on any photograph from which a line cut is to be made.
Tacks and pins have been used on maps to locate agencies, salesmen, customers, etc., more than for any other one purpose. The various possibilities in applying tacks and pins to sales-department work cannot be thoroughly covered here, but if a few general methods are known, each sales manager can work out for himself the pin scheme which best suits his own conditions.
Fig. 191 was photographed, without any retouching, direct from a section of the United States Geological Survey topographical maps. These contour maps, having a scale of about one inch to the mile, may be obtained from the Geological Survey at Washington, for most of these sections of the country which are thickly settled. The maps are very low in cost and yet are remarkably accurate. Fig. 191 was
