MAPPING.

Mapping is the art of delineating the surface of the ground, and embellishing it to represent the natural appearances by colours, making the whole descriptive.

To excel in this art as a perfect draughtsman, a knowledge of landscape drawing will assist greatly in colouring the various parts to give it a natural effect.

The different styles of printing should be well studied. Great neatness is also required in drawing with the compasses, scale border, &c. Sometimes an abstract reference of the quantities is introduced, representing a scroll of paper and a vignette of some particular object on the estate.

Plans drawn on vellum or parchment are more difficult in executing, and never to be depended upon for accuracy after, both being effected by atmospheric influence more seriously than paper.

For practical purposes, surveys should never be plotted to a less scale than three or four chains to the inch; for convenience they may be reduced to any scale, by the following different methods:

The most perfect instruments for reducing plans are the eidograph and pentagraph. The proportional compass is a most valuable instrument, particularly for enlarging or reducing buildings, &c. (See Instruments, Part V.)

The system of reducing by squares or triangles, laid down to their respective scales, although tedious, is very accurate.

Enlargement of plans should never be done by the pentagraph; either re-plot from the field-book, or by triangles and squares.

In copying plans there are various methods; the two following are the best: The paper being confined to the drawing board, lay the original plan over it; then with a fine needle prick through all the lines and buildings; draw pencil lines through all these points and ink them in.

The next method is, to lay a piece of tracing paper over the plan and carefully copy all the lines, &c.; then place this tracing copy smoothly on the paper prepared for the new plan; underneath the tracing place a sheet of very thin tissue paper prepared either black or red, and with a very fine-pointed ivory tracer go over all the lines, and prick off all the buildings with a fine needle; the impression of coloured paper will be left. This is the most expeditious mode.

Another method is sometimes used, applicable only to small drawings. Provide a large sheet of plate-glass (which should be mounted in a frame), upon which the original plan and the paper is fixed in such a position to receive the strongest light; the lines are then visible through the paper, and traced off with a hard pencil.

A north light is best for an office, in which should be firmly fixed up a strong drawing board; provide also several other drawing boards made to the different sizes of drawing paper; also several T squares, and angle or set squares, straight edges, centrolineads for perspective, &c.

be

The beam-compass is a most necessary instrument in plotting large surveys. The most approved is the French invention. The sliding boxes are packed in a small case; the beam may made by any carpenter-simply a straight piece of wood made to fit the boxes, and of the length required. They are far more convenient than those that are divided with verniers and tangent screws.

A box of curves or arcs of circles is useful, not only for drawing curves of railways, but for architectural drawings of arches and other purposes. They are made of hard wood, from half an inch to any radius, which is always marked on them therefore, whatever the radius is on the ground according to the scale of the plan, so is the number of the curve, as thus: Multiply the number of chains radius to the curve by the number of chains to the inch the plan is drawn.

Suppose the plan to be 3 chains to the inch, and the curve

20 inches, then 20 × 3 = 60 chains, or of a mile. Again, if the curve is 40 inches, and the plan 4 chains to the inch, then 40 x 4 = 160 chains, or 2 miles radius; and so on.

In highly finished plans, the hills are shaded or stippled with light Indian ink, or short curved lines, repeated so as to vary the depth of shade.

In like manner the ploughed lands are represented by drawing narrow parallel lines representing the furrows. To represent gravel, mix light Indian ink, with a toothbrush by the finger slightly touch the hairs, and spirt it over the part required, having first cut out a piece of paper the form of the piece, to protect other parts of the drawing from being injured.

MERIDIAN LINE.

The magnetic meridian does not show the true north, which is always moving so many degrees east or west, called the variation (at present it is about 23° 15′ west).

When a compass is drawn on a finished plan, the true north is generally drawn from the meridian line.

There are several methods of finding the variation by astronomical problems, seldom resorted to or required by surveyors in their ordinary course of business.

The most simple and ready method (see Fig. 4, Plate 35) is, by drawing on a perfect smooth and level plane, open to the morning and afternoon sun, three or four concentric circles; in the centre of the circles fix a straight piece of wire truly perpendicular, of such height that its whole shadow may fall upon all the circles at equal hours before and after twelve o'clock.

From about eight o'clock in the morning until four o'clock in the afternoon, about which hour the extremity of the pin's shadow will fall without the circles, particularly note the time. in the forenoon when the extremity of the shortening shadow's point touches the several circles, and then make marks.

In the afternoon of the same day, and the same distance of time from twelve o'clock, watch the lengthening shadows as before, making marks on the circles where the shadow falls.

Lastly, find the middle point exactly between two marks on the same circle, and draw a line from the centre through that point, which will be the true meridian line or north point.

Remove the pin, and fix a short-pointed pin in its place, on which place the magnetic needle; when it is at rest, mark the point it cuts on one of the circles at the north end; from that point draw another line through the centre, measure that angle accurately, which will be the number of degrees' variation. To measure the angle, see Problem 14.

DIVISION OF LAND.

The division of land is applied to many cases; as the general inclosure of a parish in which there are sundry claimants, each receiving land in proportion to their claims, the quantity being guided by the value per acre.*

In some cases an exchange of land is made between two adjoining proprietors for the mutual improvement to their estates, taking value for value, or quantity for quantity.

In either case it requires a correct system to arrive at a true balance, therefore a division has to be made according to circumstances, to accomplish which the following examples are given.

In small plots of level ground having straight fences, whether rectangular or triangular, there is no difficulty in laying out a division without a plan, as the dimensions required for the calculation can be made at the same time the division is made.

In all other cases an accurate plan, and quantity of the land

*Whatever the value is per acre, in calculating it must be reduced to shillings and decimals, to obtain an accurate result, in the same manner as the quantities are entered. The value per acre is usually marked in private characters, such as letters of any particular town or object, containing the exact number of letters in lieu of figures, as "Altringham," "Mayflower," &c.

to be divided, must be made before any calculation can be made, or the allotments staked out.

To facilitate the calculations required in the divisions, see Tables, Nos. 11 and 13.

Fig. 1, Plate 27.

Problem 36.

Example 1. It is required to cut off 1 acre 3 roods from a parallelogram containing 3 acres, parallel to the side A B, equal to 600 links. See Table 13.

Rule. Divide the square links in the quantity to be cut off, by the number of links in the side; the product will be the length of the other side; thus:

1.75000 600 = 292 links

Note.-Explanation to Table 13. The first column shows the number of acres, the second column the number of square links contained in the required number of acres; the roods and perches the same; each part is taken out separately and added together.

Fig. 2, Plate 27.

Problem 37.

Example 2. It is required to cut off 2 acres from a rectangular piece of ground, containing 3 acres 2 roods 16 perches, from a fixed point at a.

Rule. Draw an assumed line, as a b; then find the quantity of a b CD equal to 2.550; that being an excess of .55000 square links, therefore divide that sum by half the length of a b, equal to 620 links; the product will be 88 links (nearly), provided it was to be set out parallel; the figure of the excess, a b c, being a triangle, the perpendicular cd will then be 176 links; then will a c C D be the quantity required.

Fig. 3, Plate 27.

Problem 38.

Example 3. To divide a piece of building land of a rectangular figure, containing 6 acres 3 roods, between A B C, being of equal value per acre; the proportionate share of A equal to 7 parts, B = 5 parts, and C = 3 parts.