Depicting of statistical data in the form of attractive shapes such as bars, circles, rectangles is called diagrammatic presentation. 

A diagram is a visual form of presentation of statistical data, highlighting their basic facts and relationship. There are geometrical figures like lines, bars, squares, rectangles, circles, curves, etc. Diagrams are used with great effectiveness in the presentation of all types of data. 

When properly constructed, they readily show information that might otherwise be lost amid the details of numerical tabulation. 

Importance of Diagrams : 

 A properly constructed diagram appeals to the eye as well as the mind since it is practical, clear and easily understandable even by those who are unacquainted with the methods of presentation. Utility or importance of diagrams will become clearer from the following points - 

(i) Attractive and Effective Means of Presentation : Beautiful lines ;full of various colours and signs attract human sight, and do not strain the mind of the observer. A common man who does not wish to indulge in figures, get message from a well prepared diagram.

(ii) Make Data Simple and Understandable : The mass of complex data, when prepared through diagram, can be understood easily. According to Shri Morane, “Diagrams help us to understand the complete meaning of a complex numerical situation at one sight only”. 

(iii) Facilitate Comparison : Diagrams make comparison possible between two sets of data of different periods, regions or other facts by putting side by side through diagrammatic presentation. 

(iv) Save Time and Energy : The data which will take hours to understand, becomes clear by just having a look at total facts represented through diagrams. 

(v) Universal Utility : Because of its merits, the diagrams are used for presentation of statistical data in different areas. It is widely used technique in economic, business, administration, social and other areas. 

(vi) Helpful in Information Communication : A diagram depicts more information than the data shown in a table. Information concerning data to general public becomes more easy through diagrams and gets into the mind of a person with ordinary knowledge.