Landscaping and Gardening.info

As with our previous lessons in landscaping, this lesson provides more of the basics for doing the actual landscaping. This one gives you different methods for how to enlarge and reduce the plans you may have created or received in the previous lessons on landscaping.

LESSON 6

ENLARGING AND REDUCING PLANS

THE purpose of this lesson is to teach the pupil how to enlarge or reduce plans or maps, that is how to redraw them at a larger or a smaller scale. There are several methods of doing the work, anyone of which may be used for either enlarg­ing or reducing. Some of the methods are sim­ilar to those used in making surveys, for surveying is simply reducing a plan from full size to some smaller scale.

Cross-Section Method

The plan to be enlarged or reduced is ruled off with two sets of parallel lines at right angles to each other equally spaced, usually at some multiple of five or ten feet apart at the scale of the plan. The lines in one direction are numbered and those in the other direction lettered. The sheet on which the enlargement or reduction is to be made is then ruled off in the same way, the lines being spaced relatively the same distance apart, that is the same number of feet apart at the new scale and numbered and lettered as on the original plan. The lines and objects of the plan are then drawn in each square in their relative positions, the distances being scaled or es­timated depending on the accuracy required. This method is similar to a cross-section survey.

The Radial Method

A transparent paper or cloth is firmly tacked down over the plan so that they will not move on one another. A point, usually somewhat central in location, is then taken from which the distance is measured, at the scale of the original, along a straight line to any
object on the plan beneath. The position of the object is then located on the tracing paper or cloth along the same line and at rela­tively the same distance from the central point at the new scale. Instead of changing the scale each time it is often easier to multiply the original reading by the ratio of enlargement or reduction and plot the point without moving the scale. This method is similar to the work done at anyone station of a stadia-transit surveyor a plane-table survey.

Parallel Courses and Proportional Measurements

In reducing or enlarging a simple rectilinear outline drawing as of a building, field or outline survey, a very easy method is to tack a transparent paper or cloth over the drawing, then starting from some angle draw a line directly over the first side and of the required length at the new scale, draw through its end a line parallel to the second side and measure off the required proportional length.

Continue in this way making the corresponding sides of the original and the new drawing parallel and proportional. The last course will coincide with the last course of the original and its farther end will coincide with the starting point. Lines drawn from the starting point through any angle of the new plan will pass through the corresponding angle of the original.

A starting point may be taken and all the work done entirely to one side or within the original so long as all corresponding sides are drawn parallel and proportional. This method of reducing is similar to the use of the plane-table or oriented drawing board in locating a broken line from successive stations. It is merely a little different application of the radial method.

The Pantograph Method

The pantograph is a mechanical device consisting of two pairs of parallel bars so arranged that a pencil mounted on one bar will move in any direction at a definite relation to the motion of a tracer
point mounted on another bar. The ratio of this relation may be varied by adjusting the bars, the pencil and the tracer point to various positions. When the tracer is drawn along the lines of a
plan the pencil will reproduce the plan at a pro­portionately larger or smaller scale. When the pencil describes the larger motion the new plan will be an enlargement but if the pencil and tracer are transposed in position so that the pencil describes the lesser motion the new plan will be a reduction. This method is simply a mechanical application of the radial method, the fixed end of the pantograph bars corresponding to the central point used in that method.

Proportional Dividers

This is a mechanical device having two legs which cross at a movable pivot and open pro­portionally on opposite sides of it; this proportion may be varied by moving the pivot back or forth along the legs of the instrument. When adjusted so as to give the desired ratio the pivot is clamped in place and measurements taken off the original plan with one end of the instrument are plotted on the new plan with the other end.

This is not so much a separate method of enlargement or reduction as it is an instrument which may be made use of in any other method. This method is one of the most practicable of all.

Equipment

For practice in reducing and enlarging the pupil should have several maps and plans of various sizes available. He must have an engineer’s scale, with the necessary drawing board, T-square, triangle, pencil, etc. If the pantograph method is to be illustrated it will be necessary of course to have a pantograph; and a set of proportional dividers will be required in learning method 5 above.

Practice

The student should redraw several maps and plans, reducing some, enlarging others. Plans in this book will serve admirably, as many of them will have to be redrawn by the pupil as the course proceeds.
This practice need not be unduly protracted, since there will be many occasions for the further use of the methods here described, but the pupil should spend enough time in this work so that he can use several different methods readily.

Tommorrow we will include a couple more of our landscaping tips if time permits.