Certain contour lines are commonly accentuated on a map, generally every fourth or fifth line—that is, for a 10-foot interval every 50-foot line, for a 20-foot interval every 100-foot line, for a 25-foot interval every 100-foot line, for a 50-foot interval every 250-foot line, and for a 100-foot interval every 500-foot line.
Hachuring.—The effect of relief can be produced satisfactorily by hachuring but only by a draftsman who has had considerable well-directed practice in that kind of drawing. In a hachured map the light should seem to come from the west or northwest—that is, the darker parts should be on the east or southeast side of an elevation and the lighter parts on the west or northwest The highest elevation should be represented by the darkest shade on the right and by a corresponding high light on the left. The hachuring should begin at the crest of a peak, range, or butte and be worked downward toward the gentler slopes, the lines being drawn farther apart and made thinner until the floor of the valley is reached and the effect of shadow is lost by fewer and lighter lines. On a hachured map that is made from a contoured map somewhat definite differences of elevation may be indicated by the intervals between the strokes, and abrupt changes in slope may be indicated by shorter and heavier lines. The strokes should be disjointed, and they should trend at right angles to the upper margin of a cliff and should radiate from a peak. [Figure 6, B], represents satisfactory hachuring.
Hill shading.—Relief is more easily expressed by shading than by hachuring. (See [fig. 6, C, D].) The draftsman can best express it by this means after he has studied contoured maps or photographs of the region mapped, if they are available, in order that he may obtain an idea of the details of its topography.
The special means used to produce hill shading will depend on the character of surface of the paper on which the drawing is to be made, the size of the map, the amount of detail and refinement of execution desired, and the amount of reduction to be made in reproducing the drawing. For maps on which it is desired to show some refinement of drawing and detail, a lithographic or wax crayon can be used on paper which has a grained surface. The draftsman must express relief according to the information he has at hand, whether detailed or general, and must employ methods that accord with the purpose of the map and the mode of reproduction selected. If a shaded relief map is to be prepared for direct reproduction by photolithography and the shading is to be printed in a separate color the base map should be completed first and a light photographic or blue print obtained on which to add the relief in black lithographic crayon, to insure perfect fitting of the relief and the base; or the relief can be prepared on an oversheet—a semitransparent white paper with sufficient "tooth" or grain to cut the shading up into minute dots. The shadowless drafting table (see [p. 47]) is especially useful for this purpose. On this oversheet register marks should be placed at the four comers and at several other points, particularly at the intersection of parallels and meridians.
For relief shading on small black and white maps Ross's hand-stipple drawing paper may be used. (See [p. 24].) By rubbing a black wax crayon or pencil over the surface of the paper the desired effect is produced in fine dots or in stipple, which may be varied in density of shade at the will of the draftsman. (See [fig. 6, C].) High lights can be produced by scraping away the chalky surface of the paper. A lithographic or wax crayon is the best medium to use on this stipple paper, as on the paper referred to in the preceding paragraph, for the shading produced by it is not so easily smeared as that produced in pastel or by a graphite pencil. The object of using either the rough paper or Boss's stipple paper for drawings that are to be reproduced by photo-engraving is to produce a shading that is broken up into dots of varying sizes, which is essential in such reproduction.
Belief shading for maps can also be made with a brush in flat washes of either india ink or lampblack. Such shading should be made only over a blue print or an impression of some kind from the map upon which the shading or relief is to be overprinted. If the relief is expressed on the author's original by contours the general shapes of the relief and the drainage lines can be traced and transferred lightly in blue lines to form a base on which to model the shading and at the same time to make the shading fit the streams. Such a drawing can be photographed through a screen and reproduced by half tone (see [fig. 6, D]) or mezzotint as a separate plate made to overprint the map in another color.
HYDROGRAPHY.
General directions.—The drainage features of a map should be so drawn as to suggest the natural courses of the streams. Streams should not be drawn in straight, hard lines, as such lines are decidedly unnatural and produce a crude effect. The course of a river may be straight in general, but it is likely to be somewhat sinuous in detail. If the streams shown on a preliminary map are drawn in a clumsy or characterless fashion they should be redrawn with a freehand effect or made slightly wavy, in order that they may appear more natural. The gradual widening of streams from source to mouth should also be shown in the drawing. On small-scale maps, where the eye can at once see a stream through its full length, this almost imperceptible widening can be expressed by a line of almost uniform weight except for the stretch near the source, where it should grow thinner and taper off. On maps which are to be reproduced directly from drawings in black and white and which are to show both contour lines and drainage the lines representing the streams and other water bodies should generally be drawn freehand and slightly heavier than the contour lines, which should be sharper and more precise.
The names of all streams or other bodies of water should be in italic letters, those of the larger streams being lettered in capitals and those of the smaller streams in capitals and lower-case letters. (See "Lettering," [p. 53].)