# Pie Charts

## Introduction

Pie charts are used to show data involving percentages. For example, the global use of different energy sources. Although you will not use them too frequently in school as they are only appropriate in certain situations, it is still important that you know how to create and interpret them.

### Creating Pie Charts

We need data to create a pie chart. Underneath is a table of the nationalities of students. To create a pie chart it is best to transform the data into percentage from as we have done in the last column. First we have to divide 360° by the total of numbers (=100(%)). This tells us that each % is worth 3.6°. Start off by drawing a circle and determining a starting point by drawing a line from the centre of the circle to the outside. Then multiply the percentages by 3.6 to find the angles where the line will go. For instance 3.6 x 40 = 144. This means that the angle on the graph underneath going from the starting point (vertical line) to the next line (clockwise) is 144°. Do this for all the data. Then draw the lines, if you have not already done so and shade each region. Create a key underneath that shows what each region represents. Your should also add a title to your pie chart
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### Special Pie Charts

Sometimes, we add a second pie chart to an existing one as in the example underneath. The left pie chart is the main one and the right pie chart represents the green region on the main pie chart. This is especially useful if you have a lot of very small segments in a pie chart and is so quite overcrowded. By using a second pie chart, you can show all of these segments in detail.

## Cumulative Frequency Graphs

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