Graphs

A very big variety of graphs are used in practice. However, here we discuss only some important types of graphs which are more popular.

Technique of constructing a graph:

For constructing a graph, we make use of graph paper. Two simple straight lines are first drawn which intersect each other at right angles. The lines are commonly known as coordinate axes. The horizontal line is known as X axis or 'abscissa' and the vertical line is known as Y axis or 'ordinate'.

The Graphs of time series or line graphs

When we observe the values of a variable at various points of time, the series so formed is termed as the time series. The method of graphic presentation is extremely helpful in analyzing the change at various points of time. On the X-axis we normally take the tine and on the Y-axis the value of the variable and then join the various points by straight lines. The graph so formed is termed as the line graph. These kinds of graphs are most widely used in practice.  They are simplest to understand, easiest to make and most adaptable to many uses. They need the least technical skill and at the same time enable one to present more information of a complex nature in a perfectly understandable form than any other kind of chart; many variables can be represented on the same graph and a comparison can be made.

Graphs of one variable

When only one variable is to be shown, the X-axis measures the time and on the Y-axis the value of the variable is shown and plots the various points and join them by the straight lines. The flotation of this line represents the variations of graph that indicates the magnitude.

Band graph

A band graph is a type of line graph that shows the total successive time periods broken up onto sub-totals for each of the component parts of the total. In another words, the band graph represents, in what proportion the individual items comprising the aggregate are distributed. The various components parts are plotted one over the other and the gaps between the successive lines are filled by various shades, color, etc. so that the chart has the appearance of the series of bands. Such a chart is especially useful in dividing total sales into department, total costs into components costs, total sales into department and other such relationships.

Illustration: - Represent the following data of agricultural production by a band graph:

Solution: To draw band graph we first take cumulative figures: