Following differences may be noted between diagrams and graphs.
(1) In the construction of a graph, graph paper is used. A graph helps to study the mathematical relation between two variables such as price and demand; income and consumption, time and population etc.On the other hand, diagrams are generally constructed on a plain paper. A diagram is used for sake of comparison but not for studying the relation between two variables.
(2) Graphs are more precise and accurate than diagrams. They are more helpful to a researcher for studying the relationship between two variables and for further statistical analysis and interpretation. Diagrams furnish only approximate information on the problem under study. These are not much use to a researcher for further analysis.
(3) Graphs are used to present time series data and frequency distributions. Diagrams are useful in presenting geographical or spatial series.Presentation of data through graphs is easier than through diagrams.