Pie Chart

Pie charts have always been one of the most popular data visualisation tools. They provide simple and intuitive ways to visually represent the proportions of a whole. But what is the definition of pie chart? The pie chart meaning is a circular statistical graphical representation technique that is divided into slices that represent numerical proportions. It can illustrate percentages and proportions of data in a simplified manner. In this blog, we will look at pie chart types, examples, methods of drawing pie charts, and more.  

1.0Graph Pie Chart: Understanding its Components

A graph pie chart consists of several key components. This circular statistical graphic has various parts that go on to illustrate numerical proportions. The following describes the different parts of a graph pie chart: 

• Circle (Pie): The circle is the entire circular shape of the pie that represents the whole data set visualised in the pie chart.
• Slices: The slices of the pie chart are individual sections of the circular graph that represent the relative size of the data. 
• Arc Length: The arc length of a graph pie chart refers to the length of the curved surface of a particular slice. The larger the value, the longer the arc length. 
• Central Angle: The central angle of a slice in a pie chart is made by sectors that represent the data. The sum of all the central angles in a pie is 360°.
• Labels: The labels in pie charts provide key information about the pie sectors or slices. The various types of labels are percentage, value, annotations, etc.
• Legend: The legend of a pie chart is a visual guide that represents the colour schemes used to differentiate the pie slices. 

2.0The Formula for Pie Chart Calculation

The pie chart is an important part of data representation. It contains different segments and sectors, where each segment and sector contains some percentage of the total value. The sum of all data is 360°. 

To understand the formula for pie chart angle, you need to follow a few steps:

• You need to categorise the data.
• You need to calculate the total.
• Then, divide the categories.
• You then convert them into percentages.
• Finally, calculate the degrees for the result.

Therefore, the formula for Pie Chart angle would be:

(Given Data/Total Value of Data) × 360°

Let’s take an example of a Pie Chart to understand the concept in a detailed manner.

Example for Pie Chart Angle Calculation

Here is an example of Pie Chart with explanation to understand the concept in detail.

Problem One: Consider a survey conducted among 100 students about their favourite subjects:

• Mathematics: 50 students
• Science: 30 students
• English: 20 students

Find out the angles of each dataset of the pie chart. 

The angles are calculated as follows:

• Mathematics: (50/100) x 360 = 180°
• Science: (30/100) x 360 = 108°
• English: (20/100) x 360 = 72°

This calculation will help create a well-proportionate graph pie chart. 

Problem Two: The whole pie chart represents a value of 100. It is divided into 10 sectors/slices. The various colours represent the ingredients used to prepare this cake. What would be the exact quantity of each of the ingredients that are represented in specific colours in the following pie chart?

Solution: As we can observe, the pie is divided into 10 sectors. To calculate the exact amount of these ingredients that are added to the cake, we have to divide the whole sector's value, i.e., 100, by the number of sectors. So, 100 ÷ 10 = 10. Hence, looking at the colour divisions made in the pie chart, we can conclude that:

3.0Pie Chart with Percentages

A pie chart with percentages is a circular chart that uses slices to show the percentages of a whole. All of the slices add up to 100%. To calculate the percentages, divide the value of each category by the total sum of all the categories and multiply it by 100. The formula to express each category as a percentage would be:

(Category Value / Total Value) x 100

Problem: A small community surveyed preferred pet types. The results were as follows:

• 40 people prefer dogs.
• 30 people prefer cats.
• 20 people prefer birds.
• 10 people prefer rabbits.

Total survey participants = 100.

Calculate the percentage of people who prefer each pet type.

We all know that percentage = (Total value/Category value​)×100

The percentage of people who prefer dogs would be (40/100) x 100 = 40%

The percentage of people who prefer cats would be (30/100) x 100 = 30%

The percentage of people who prefer birds would be (20/100) x 100 = 20%

The percentage of people who prefer rabbits would be (10/100) x 100 = 10%

4.0Drawing a Pie Chart: Step-by-Step Guide

Drawing a pie chart is easy if you understand the base concepts and follow the step-by-step guide below: 

• Collect Data: Without data, there is no pie chart. Collect the data you want to work on for your pie chart.
• Calculate Percentages and Angles: Use the formulas above to calculate the percentages and angles for each category. 
• Draw a Circle: Draw a sizable circle to represent the whole dataset. 
• Use a Protractor: Use a protractor to mark the angles for each category.
• Label and Colour: Differentiate every slice with colours and labels for clarity.
• Interpret and Analyse: Use the insights from the pie chart for decision-making purposes. 

5.0Pie Chart Types

There are various pie chart types that students can benefit from. Refer to the table below to understand pie chart types, what they mean, and representative diagrams.

6.0Advantages and Limitations of Pie Charts

There are many advantages and disadvantages to using pie charts for data visualisation. Let’s look at both sides so you can make informed choices.

Advantages

• Pie charts offer a visually appealing yet straightforward way of presenting data.
• Pie charts allow you to make quick comparisons between categories.
• It is easy for everyone to comprehend and understand.

Disadvantages

• Displaying a large dataset is often not possible with pie charts.
• It might be difficult to compare smaller-sized slices.
• There is a chance of misinterpreting data because of factors like slice colours, slice orders, and presentation angles. 

7.0Conclusion

Pie charts are the most effective tool for visualising data proportions. However, they should be carefully crafted and used to avoid misinterpretations. Practice the formula for pie chart to avoid room for error.