The Protractor.-The protractor most commonly used is semicircular and made of brass or electrum. It has the advantage over the rectangular form, in that in a semicircular protractor any angle is protracted at the full length of the radius of the protractor from the centre, which is not the case with the rectangular protractor. To set off an angle with this protractor, its position will be on the right side of the north line when the bearing is less than 180°, and on the left when the bearing is greater than 180°.

B

4.50

FIG. 64.

00.9

D

To plot a Triangle. Suppose in the triangle ABC (Fig. 64) the side AC measures 6 chains, the side BC measures 4.50 chains, and the angle at B is 54°. Plot to a scale of 3 chains to one inch. Draw BC 1 inches long, take the protractor and lay down the direction of the line BD (length unknown) 54° from C. Now from centre C with radius 2 inches describe an arc cutting BD in A. Join AC. Then ABC is the triangle required. (See Fig. 64.)

A large circular protractor with vernier and arm may be used for more important work. This will enable us to measure and plot angles to 1 minute. Fig. 65 shows a one-arm circular electrum protractor, 6 inches in diameter and costing in case about £3. The length of the circumference of a circle equals 2πr, and varies as the length of the radius or the length of the protractor. It depends therefore on the length of the circumference to what degree of minuteness the circle may be

graduated. The centre of the protractor in Fig. 65 is made of glass, usually, with fine lines across it. It is therefore easy to place the centre upon the mark. One side of the arm, which is provided with a vernier, forms a radial line from the centre. The straight edge has a point fixed at the end of it which when pressed

FIG. 65.

will make a fine hole in the drawing, thus marking the exact position of the angle according to the reading of the vernier. After removing the protractor this point may be joined by a line to the central mark.

The method of using this protractor in plotting surveys made with angular instruments will be shown in a later chapter.

Level Sections.-When plotting level sections, the datum line should be parallel to the lower edge of the drawing paper. Only a Ṭ square and set square are required for this part of the work. The datum line is set off with the T square, and the vertical heights above this with the set square, which is used on the T square in a similar way to that described in connection with the plotting of offsets.

The horizontal distances are now scaled off along the datum and the vertical heights along the perpendiculars. If these perpendiculars become inconveniently long, the datum may be assumed to be so many feet above the datum of the levels. This distance is noted along the base line and written say-50 feet above datum. (See chapter on Levelling.)

Show Scale on Plan. In the case of important work it is advisable to draw the scale of the survey on the plan, because paper will expand or contract slightly in spite of the trouble that may be expended in getting it seasoned.

Surveyors' Institution Examination.—In making a survey such as the candidates for the Professional Associateship of the Surveyors' Institution are required to do, the area of the plan should be shown, besides the level sections, north point, and title. In this case where so much has to be shown on one sheet, the draughtsman may make use of any vacant spaces that may occur on the sheet, for the north point, area, and title. The plan should be in the centre of the paper, and the level sections underneath. The author prefers where possible, to show the north point as already described, so that the top of the paper represents north and the bottom south, and so forth. Conventional Signs.-Grass land is coloured green. Water is coloured prussian blue.

Cultivated land is coloured burnt sienna.

Footpaths, roads, streets, land and gravel are coloured yellow

ochre.

Buildings (brick or stone) are coloured crimson lake.
Buildings (wood) are coloured sepia.

Buildings (temporary) are coloured Payne's grey or indian ink. Some draughtsmen verge each portion of the plan with a narrow band of its respective colour but of a rather darker shade. If well done this is very effective.

Hedges and Ditches as in Fig. 66. Or draw a thin line for

FIG. 66.

I

FIG. 67.

each edge of the ditch, and sketch in elevation the hedge on whichever side of the ditch it occurs. (Fig. 67.)

The height of the bushes shown should never be more than

G

inch and should be disconnected. The ditch may be shaded in pale blue and the bushes in dark green.

Fences. All fences are usually shown on plan by a single line but if it is required to distinguish between the various kinds, this may be done as shown in the two following examples :

Wherever there is any doubt, names should be written.

Finishing up a Plan.-Any elaborate ornamentation is not to be recommended.

Printing.-Plain upright block printing (see Fig. 68) carefully done and with the letters well spaced is the best to use for titles and the names on different plots; roman or sloping block for names of roads, and italics for names of adjoining owners and details. (Fig. 69.) Printing is the most difficult part of plan-drawing to acquire, and constant practice is required.

ABCDEFGHIJKLMNOPQRS
TUVWXYZ

FIG. 68.

PLAN OF FIELDS

PLAN OF FIELDS

PLAN OF FIELDS

FIG. 69.

Border Line.-There should be a thick border line about an inch from the edge of the sheet. There are many different kinds but Figs. 70 and 71 show two good kinds.

North Point.--If any decoration is thought necessary it should consist principally of straight lines.

Methods of Enlarging, Reducing and Copying Plans

Enlarging and Reducing Plans.—1. Re-plot the plan to the scale required.

2. By squares' and proportional compasses.

3. By the Pantograph.

4. By the Eidograph.

Of these No. 1 is undoubtedly the best where there is time. No. 2 is very satisfactory, however, and is much adopted in estate offices, where the pantograph and eidograph seldom find a place, but it is not a safe method for enlarging when great accuracy is required.

By Squares and Proportional Compasses.-Take a piece of tracing paper or cloth and rule it with inch or half-inch squares, and place it on the plan to be enlarged or reduced, fastening it securely with drawing pins. Now take

A

X

D

a

B a sheet of drawing paper, and on it with very soft lead pencil rule the same number of squares to the required scale, larger or smaller as the case may be.

The copy is then made by transferring the part included in each square separately. This is done by means of the proportional compasses, which will enable us to fix each point by measuring its horizontal and vertical distance from the corner of a square. The proportional compasses are set to the proportion desired, and the rectangular co-ordinates are measured on the larger squares by the AB end of the compasses, and transferred to the smaller squares by the CD end of the compasses. (Fig. 72.)

FIG. 72.

Example.-AB, BC, CD, DE; and EC in Fig. 73 represent the fences of two fields: it is required to reduce this plan to the scale of one-half. It should be remembered that when a plan is reduced to half the scale, the area is reduced to one-fourth. Similarly, if the scale is one-third of the original, the area will be one-ninth.