Diagram are the last resorts in the hands of a statistician to present the data before the common mass, who do not understand the numerical figures, and for whom the numerical figures are considered very much boring and complicated. They take the form of geometrical figures viz.,: points, lines, bars, squares, rectangles, circles, pies, cubes, pictures, maps, charts etc. They do away with the numerical figures altogether in presenting the dry and uninteresting data in the shape of attractive, and appealing pictures which always impress and attract a man of ordinary prudence. They give a bird’s-eye-view of the whole data collected for any problem without any delay.
From the above comprehensive definition, the essential characteristics of diagrams can be outlined as under:
(i) They give a pictorial presentation of data: The diagrams give a pictorial view of the quantitative data in order that they may be more attractive and readily intelligible. Beyond this, however, they do nothing. They are not designed to prove or disprove any particular fact. They are not capable of further analysis of data.
(ii) They are concerned only with the homogeneous data: The diagrams represent only the homogeneous data which are comparable with each other. The heterogeneous data are not suitable for diagrammatic representation as they are unrelated and incomparable to each other. Similarly, a single figure is also not suitable for diagrammatic representation as it will not carry any meaningful impression for the onlooker.
(iii) They do not have any constant shape: The diagrams of any type do not have any constant shape, or size like that of the numerical figure. Their size. And shape would change with the change in scales, and the manner of presentation. Thus, it may be said that the diagram cannot to the figures.
(iv) They give only birds’ eye-view of the data: The diagrams give only a bird’s-eye-view of the data collected relating to a problems. They do not reveal the entire story of a problem as they are not capable of further and further analysis.