CHAPTER II.

CONVENTIONAL SIGNS.

(479) Various conventional signs or marks have been adopted, more or less generally, to represent on maps the inequalities of the surface of the ground, its different kinds of culture or natural products, and the objects upon it, so as not to encumber and disfigure it with much writing or many descriptive legends. This is the purpose of what is called Topographical Mapping.

(480) The relief of ground. The inequalities of the surface of the earth, its elevations and depressions, its hills and hollows, constitute its "Relief." The representation of this is sometimes called "Hill drawing." Its difficulty arises from our being accustomed to see hills sideways, or "in elevation," while they must be represented as they would be seen from above, or "in plan.” Various modes of thus drawing them are used; their positions being laid down in pencil as previously sketched by eye or measured.

If light be supposed to fall vertically, the slopes of the ground will receive less light in proportion to their steepness. The relief of ground will be indicated on this principle by making the steep slopes very dark, the gentler inclinations less so, and leaving the level surfaces white. The shades may be produced by tints of India ink applied with a brush, their edges, at the top and bottom of a hill or ridge, being softened off with a clean brush.

If light be supposed to fall obliquely, the slopes facing it will be light, and those turned from it dark. This mode is effective, but not precise. In it the light is usually supposed to come from the upper left hand corner of the map.

Horizontal contour lines are however the best convention for this purpose. Imagine a hill to be sliced off by a number of equidistant horizontal planes, and their intersections with it to be drawn as they would be seen from above, or horizontally projected on the map. These are "Contour lines." They are the same lines as would be formed by water surrounding the hill, and rising one foot at a time (or any other height) till it reached the top of the hill. The edge of the water, or its shore, at each successive rise, would be one of these horizontal contour lines. It is plain that their nearness or distance on the map would indicate the steepness or gentleness of the slopes. A right cone would thus be repreFig. 319.

Fig. 318.

Fig. 320.

sented by a series of concentric circles, as in Fig. 318; an oblique cone by circles not concentric, but nearer to each other on the steep side than on the other, as in Fig. 319; and a half-egg, somewhat as in Fig. 320.

Vertical sections, perpendicular to these contour lines, are usually combined with them. They are the "Lines of greatest slope," and may be supposed to represent water running down the sides of the hill. They are also made thicker and nearer together on the steeper slopes, to produce the effect required by the convention of vertical light

already referred to. The marginal figure shews an elongated half-egg, or oval hill, thus represented.

The spaces between the rows of vertical

"Hatchings" indicate

Fig. 321.

the contour lines, which are not actually drawn. The beauty of the graphical execution of this work depends on the uniformity of the strokes representing uniform slopes, on their perfectly regular gradation in thickness and nearness, for varying slopes, and on their being made precisely at right angles to the contour lines between which they are situated.

:

The methods of determining the contour lines are applications of Levelling, and will therefore be postponed, together with the farther details of "Hill-drawing," to the volume treating of that subject, which is announced in the Preface.

(481) Signs for natural surface. Sand is represented by fine dots made with the point of the pen; gravel by coarser dots. Rocks are drawn in their proper places in irregular angular forms, imitating their true appearance as seen from above. The nature of the rocks, or the Geology of the country, may be shown by applying the proper colors, as agreed on by geologists, to the back of the map, so that they may be seen by holding it up against the light, while they will thus not confuse the usual details.

(482) Signs for vegetation. Woods are represented by scol

loped circles, irregularly disposed, imitating trees seen "in plan," and closer or farther apart according to the thickness of the forest. It is usual to shade their lower and right hand sides and to represent their

Fig. 322.

shadows, as in the figure, though, in strictness, this is inconsistent with the hypothesis of vertical light, adopted for "hill-drawing." For pine and similar forests, the signs may have a star-like form, as on the right hand side of the figure. Trees are sometimes drawn "in elevation," or sideways, as usually seen. This makes them more easily recognized, but is in utter violation of the principles of mapping in horizontal projection, though it may be defended as a pure convention. Orchards are represented by trees arranged in rows. Bushes may be drawn like trees, but smaller.

Grass-land is drawn with irregularly scattered groups of short lines, as in the figure, the lines being arranged in odd numbers, and so that the top of each group is convex and its bottom horizontal or parallel to the base of the drawing. Meadows are sometimes represented by pairs of diverging lines, (as on the right

Fig. 323.

ーコニー

Mill

۷۷۷

حنا الله

A

۷۷۷

VVV

الله الله

۷۷۷

اله

اللا

Cultivated land is

Fig. 324.

of the figure), which may be regarded as tall blades of grass. Uncultivated land is indicated by appropriately intermingling the signs for grass land, bushes, sand and rocks. shown by parallel rows of broken and dotted lines, as in the figure, representing furrows. Crops are so temporary that signs for them are unnecessary, though often used. They are usu- 111....... ally imitative, as for cotton, sugar, tobacco, rice, vines, hops, &c. Gardens are drawn with circular and other beds and walks.

(483) Signs for water. The Sea-coast is represented by drawing a line parallel to the shore, following all its windings and indentations, and as close to it as possible, then another parallel line a little more distant, then a third still more distant, and so on. Examples are seen in figures 287, &c. If these lines are drawn from the low tide mark, a similar set may be drawn between that and the high tide mark, and dots, for sand, be made over the included space. Rivers have each shore treated like the sea shore, as in the figures of Part VII.* Brooks would be shown by only two lines, or one, according to their magnitude. Ponds may be drawn like sea shores, or represented by parallel horizontal lines ruled across them. Marshes and Swamps are represented by an irregular intermingling of the preceding sign with that for grass and bushes, as in the figure.

Fig. 325.

AR

(484) Colored Topography. The conventional signs which have been described, as made with the pen require much time and labor. Colors are generally used by the French as substitutes for them, and combine the advantages of great rapidity and effective

Only three colors (besides India ink) are required; viz. Gamboge (yellow), Indigo (blue), and Lake (pink). Sepia, Burnt Sienna, Yellow ochre, Red lead, and Vermillion, are also sometimes used. The last three are difficult to work with. To use these paints, moisten the end of a cake and rub it up with a drop of water, afterwards diluting this to the proper tint, which should always be light and delicate. To cover any surface with a uniform flat tint, use a large camel's hair or sable brush, keep it always moderately full, incline the board towards you, previously moisten the paper with clean water if the outline is very irregular, begin at the top of the surface, apply a tint across the upper part, and continue it downwards, never letting the edge dry. This last is the secret of a smooth tint. It requires rapidity in returning to the beginning of a tint to continue it, and dexterity in following the outline. Marbling, or variegation, is produced by having a brush at each end of a stick, one for each color, and applying first one, and then the other beside it before it dries, so that they may blend but not mix, and produce an irregularly clouded appearance. Scratched parts of the paper may be painted over by first applying strong alum water to the place.

The conventions for colored Topography, adopted by the French Military Engineers, are as follows. WOODS, yellow; using gamboge and a very little indigo. GRASS-LAND, green; made of gamboge and indigo. CULTIVATED LAND, brown; lake, gamboge, and a little India ink. "Burnt Sienna" will answer. Adjoining fields should be slightly varied in tint. Sometimes furrows are indicated by strips of various colors. GARDENS are represented by small rectangular patches of brighter green and brown. UNCULTIVATED LAND, marbled green and light brown. BRUSH, BRAMBLES, &c., marbled green and yellow. HEATH, FURZE, &c., marbled green and pink. VINEYARDS, purple; lake and indigo. SANDS, a light brown; gamboge and lake. "Yellow ochre" will do. LAKES and RIVERS, light blue, with a darker tint on their upper and left hand sides. SEAS, dark blue, with a little yellow added. MARSHES, the blue of water, with spots of grass green, the touches all lying horizontally. ROADS, brown; between the tints for sand and cultivated ground, with more India ink. HILLS, greenish brown; gamboge, indigo, lake and India ink, instead of the pure India ink, directed in Art. (480). WOODS may be finished up by drawing the trees as in Art. (482) and coloring them green, with touches of gamboge towards the light (the upper and left hand side) and of indigo on the opposite side.