When the given data is represented by the sector of a circle, a pie chart or the graph is formed.
Pie Chart
Sector: - Central angle is the angle when vertex is the centre of the circle and the region of the circle that is enclosed by the arms of the angle is called sector.
Method of Constructing a Pie Chart
Graph is a simple way of understanding and interpreting of the situation represented by the given frequency distributions. A pie chart is the type of graph in which the data is represented by the sectors of a circle.
After constructing a circle of an appropriate radius or diameter, sectors of the circle are made. From the north of the circle the first sector should be made in a clock wise direction. This looks more attractive and easily understandable, as the angle of the sectors goes on decreasing as we see the pie chart in a clock wise direction, staring from the North.
The first sector should represent the biggest angle calculated from the data given, then the subsequent smaller sectors are drawn. If the data has to be represented in percentage, divide the circle into hundred equal parts. This will give the data representation in percentage. This provides a better representative effect, in the fact that one can compare the differences between the values displayed on the pie chart easily
Example of Pie Chart
Question:-
For the given rainfall distribution from year 2005 to 2009, construct a pie chart after calculating the degrees of each sector to be drawn:
Rainfall of a place in the last five years (in centimeters):-
1. 2005 ? 64.8 cm
2. 2006 ? 61.4 cm
3. 2007 ? 68.5 cm
4. 2008 ? 76.2 cm
5. 2009 ? 69.9 cm
Solution:-
Conversion of cm into degrees:-
Average annual rainfall in the last five years (from 2005 to 2009):-
64.8 + 61.4 + 68.5 + 76.2 + 69.9 = 340.8 cm
Therefore 340.8 cm rainfall is similar to 360 degrees on the pie chart.
YearsRainfall in cmConversion of rainfall into degreesDegreesApproximate Degrees