Another way of preparing a two-dimensional diagram is in the form of circles. In such diagrams both the total and the component parts or sector can be shown. The area of a circle is proportional to the square of its radius. As in the construction of squares, the square-roots of various figures are worked out while constructing the circle. However, in the latter case the radii of the circles can be obtained by dividing the value of pie and taking square-root.
Circles can be used in all those cases in which squares are used. However, in both these types of diagram it is difficult to judge the relative magnitudes with precision.
Circles are difficult to compare and as such are not very popular in statistical work. When it is necessary to use circles, they should be compared on an area basis rather than on a diameter basis, as the diameter basis is very misleading. Compared to rectangles, circles are more difficult to construct and interpret.