Εικόνες σελίδας
PDF
Ηλεκτρ. έκδοση

CHAPTER X

GRAPHICAL REPRESENTATION

It frequently happens that an idea can be expressed very much more clearly and briefly by a drawing than by words. Thus, the idea of a square is conveyed instantly by a picture of a square ■. The drawing or diagram is called a graphical representation.

Many illustrations of this sort are doubtless already familiar to the student. Tally marks, THL, the indication of the hours on the clock-face by the numerals, I, II, III, IIII, etc., the determination of the pitch of a note by its location on the musical staff,

diminuendo

[ocr errors]

the

crescendo sign etc., are all graphic in character, as also are the indication of direction

conven

for railroad,

by an arrow →, the north and south line tional signs used in map drawing, like + WWW for grass, astronomical symbols such as for earth, for moon, the symbols of geometry, ▲ for triangle, O for circle, and the like.

A geographical map is an example of line representation wherein distances are plotted to some convenient scale. In every case the scale used will depend upon the amount of territory to be shown and on the desired size of the map itself.

Line representation is the basis of drawing and of all mechanical work. The floor plan of a house, for example,

[graphic]

NATIONAL CAPITOL AT WASHINGTON, D. C.

and its elevation, are graphical representations of the location of walls, doorways, windows, etc. The accompanying figures show a general view of the National Capitol together with its floor plan.

[graphic][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][subsumed][merged small]

Such data as valuation of exports and imports, increase in population, relative lengths of rivers, heights of mountains, changes in temperature, amounts of rainfall, variations in the price of foodstuffs, and the like, can be presented much more effectively by means of diagrams than by columns of figures.

[blocks in formation]

A relation like that which exists between the speed of a vehicle and the time spent in traveling one mile is best shown diagrammatically, as in the accompanying figure.

Graphic diagrams are of a great variety of forms, and in determining upon the scheme of representation to be used in a particular case, the student should select that type which will set forth in the most telling fashion the essential facts of the data to be presented.

[ocr errors]
[graphic]

Exercise

1. Using the figures in the table below, prepare a graphical diagram showing the relative population of the world's largest cities.

POPULATION OF THE WORLD'S LARGEST CITIES

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

2. Using the figures in the table below, prepare a diagram showing the population of the United States at each census.

POPULATION OF THE UNITED STATES AT EACH CENSUS

[blocks in formation]

Sometimes a circular area divided into sectors offers itself as the best means of setting forth data, especially if the relation is a simple one.

[blocks in formation]

Illustrations of this type

are shown in the accompanying diagrams. The first sets forth the facts of ground utilization in European Russia; the second shows to what extent the annual cut exceeds the annual forest growth in the United States.

For laying out the angles at the centers of the circles in such diagrams as these, an instru

ment called a protractor is sometimes used. By joining the notch 0 of the protractor to each graduation mark, a set of angles is obtained at 0 of one degree each.

[blocks in formation]

the angle then indicates on the protractor the number of degrees in the angle.

To draw an angle of a given number of degrees, place the base of the protractor along a straight line and mark on

« ΠροηγούμενηΣυνέχεια »