Pie Chart
A pie chart is a type of graph that displays data in a circular graph. The pieces of the graph are proportional to the fraction of the whole in each category. In other words, each slice of the pie is relative to the size of that category in the group as a whole. The entire “pie” represents 100 percent of a whole, while the pie “slices” represents portions of the whole.
The following chart shows water usage. You can see that toilet water usage is greater than shower water usage because the piece of the “pie” is greater:
What is a Pie Chart?
A pie chart is a circular chart
(diagram) divided into sectors which are in proportion. Each sector represents
a proportionate part of the whole, and the total value of the pie is always 100
percent.
Pie charts can make the size of
portions easy to understand at a glance. They are widely used in business
presentations and education to show the proportions among a large variety of
categories including expenses, segments of a population or answers to a survey.
How to Draw a Pie Chart?
Steps for Constructing a Pie Chart
1. Draw a circle of an appropriate radius
and draw its one radius.
2. Starting with this radius, draw
sectors with different central angles as required.
3. Shade each sector using different
colours and label them.
4. Give a title to the pie chart.
To construct a pie chart:
·
Gather the data. Pie
charts depict percentages. Make sure your
percentages add up to 100% and get rid of any rounding issues that would make
the total something other than 100%.
·
You can find the
percentage of a data value by using the formula percentage = (data value/total
value) * 100.
·
You can find the angle
of the sector at the center by using the formula angle = (percentage/100) * 360.
·
You can also find the
angle of the sector at the center by using the formula angle = (value of the
sector/sum of all the values) * 360.
·
Consider creating a
legend. If a wedge is too small to hold
text, you can create a label and draw a line identifying the appropriate slice.
Alternatively, you can create a key that shows what each color represents.
Tips for Creating Better Pie Graphs
1.
Please do
not use more than 5 slices in any pie chart otherwise it becomes too hard to
read.
2. Please do
not use a pie chart if the values of the sectors are close to each other and
it's important to see the differences. For example, 32%, 33% and 35% will look
pretty even at a glance when illustrated on a pie chart. Using a bar chart will
make the differences more obvious.
3. Please do
not use a pie chart if what you're comparing are not parts of a whole. For
example, it makes sense to use a pie chart to compare the profitability of
different divisions inside a larger enterprise. Categories on the pie chart
must be mutually exclusive and not overlapping.
Examples on Pie Chart
Example 1: The
following table shows the choice of restaurants for students of class VIII.
|
Restaurant
|
A
|
B
|
C
|
D
|
E
|
|
No. of students
|
24
|
18
|
16
|
20
|
12
|
Represent the above
information by using a pie chart.
Solution: Total number of students = 24 + 18 + 16 + 20 + 12 =
90
Calculate the central angle for each data values as follows:
Now,
1. Draw a circle with a
convenient radius and draw a radius as the starting point.
2. Use a protractor to draw the
sectors corresponding to the central angles calculated.
3. Label each sector
according to the item it corresponds to and their respective angles.
Example 2: The
following table shows the production of motorbikes in a factory in five
consecutive months.
|
Month
|
June
|
July
|
August
|
September
|
October
|
|
Production
|
420
|
510
|
190
|
240
|
440
|
Represent the above
information by using a pie chart.
Solution: Total number of students = 420 + 510 + 190 + 240 + 440
= 1800
Now, we will find the
central angles for each month to draw the pie chart.
June = 420/1800 × 360° = 84°
July = 510/1800 × 360° = 102°
August = 190/1800 × 360° = 38°
September = 240/1800 × 360° =
48°
October = 440/1800 × 360° = 88°
Now, draw the pie chart as follows: