The Preparation of Illustrations for Reports of the United States Geological Survey / With Brief Descriptions of Processes of Reproduction

by John L. Ridgway

U. S. GEOLOGICAL SURVEY

PREPARATION OF ILLUSTRATIONS PLATE VIII

PATTERNS USED TO SHOW DISTINCTIONS BETWEEN AREAS ON BLACK AND WHITE MAPS
Contrasts may be increased by varying the direction and spacing of Lines

SYMBOLS.

Symbols should be drawn with as much care as letters, though to a critic they may not appear so bad as poor lettering unless he finds them glaringly large or so small that he can discover or identify them only with difficulty. The size of a symbol must depend on its importance on the map bearing it. On a map that shows numerous mines, for instance, the crossed hammers or the symbols for shafts should be not only visible but conspicuous. The draftsman who is to make such a map must know beforehand how much his drawing will be reduced in reproduction and must make the symbols in proportion to the reduction. The symbols shown in [Plate II] ([p. 20]) should be used in all the Survey's illustrations where they are appropriate.

AREAL PATTERNS FOR BLACK AND WHITE MAPS.

The conventional patterns used on a map to distinguish separate areas, chiefly geologic, are shown in [Plate VIII]. The patterns shown represent the proper combinations of lines, dots, and other forms and should be spaced openly or closely according to the size of the area covered, the contrast needed between areas, and the general clearness and effect desired. If a map is to show both small and large areas dense or closely spaced patterns should generally be used for the smaller areas, even if they may be required for some fairly large areas representing the same formation or condition. On the other hand, open patterns should be used for large areas. Again, it may be necessary to make certain areas more conspicuous than others, and this effect can be best produced by drawing the lines closer together rather than by making them heavier, unless the area covered is small or unless a closely spaced similar pattern has been or will be used elsewhere on the map. Heavy-line patterns or bars are not desirable. The lines forming a pattern should generally be drawn at an angle of 45° to the sides of the map; they should be drawn vertically or horizontally only in small areas or in areas not crossed by meridians or parallels or by other lines running in the same direction. The lines should preferably run across the long axis of an area, not parallel to it, and the predominating trend or general direction of the areas of one geologic formation on a map should decide the direction of the lines for all areas of that formation on the same map, even if the rule must be violated on some of the minor areas.