Radar chart: Representing your multivariate data in an effective manner

Bar charts, pie charts, and line charts are the popular data representation tools well-known to a researcher. But there is a lesser known visually powerful chart out there that packs a lot of information into a single image, the radar chart. 

Radar chart also known as spider or polar chart is a 2D chart is a way of presenting multivariate data (quantitative). Simply said, they are utilised to plot one or more groups over multiple common variables. 

This is done by giving each variable an axis (arranged radially around the center point) and plotting the data as a polygonal shape. As a result, this chart looks like several irregular polygons stacked together with the same center point. 

Typically, the data from multiple observations are placed in a single chart thereby overlaying them, minimising the opacity of each polygon and displaying multiple polygons.

In addition to presenting the multivariate data, radar charts can also be used to compare multiple items against multiple criteria. For instance, you can use this chart to determine how humidity changes in multiple locations over the course of a month.

For example, consider the examination marks of Shirley. The marks ranges from 0 to 20 in mathematics, statistics, biology, etc. Using radar chart you can determine in which subject did Shirley score well and which topics need improvement.

In the above radar chart all axes have the same origin. However, in many cases the relative position and angle of the axes are not informative. Each axis share same scale but the range of variable values vary between the displayed variable values. 

In the above mentioned example the performance of only one student is represented. A similar chart can be used to compare marks of more than one student. For instance,  

Here by comparing the scores of Sonia and Shirley, we can determine that except for english, sports and R-coding, Shirley has performed well in examination when compared to Sonia.

When should you consider using radar chart?

There is a false belief that radar chart or spider chart can be used whenever it is required to present the multivariate data. But the fact is, it can be used under the following circumstances.  

  1. When you want to compare several items with more than 5 metrics of characteristics - The distinctive characteristic of radar chart is its ability to make general comparison of all the metrics to arrive at a judgement. It allows you to decide the sharp points, cover area on the metric lines and obtain an overall understanding of pros & cons of the items you intend to judge. 

For example, comparing the highest score of various subjects in different sections. 

 

  1. The comprehensive situation of different items - 

Radar charts is the ultimate choice if you intend to view the coverage of each item under different metrics as it allows each item to cover a fixed area depending on its data. 

For instance, if a coach wants to see the performance of his players’, he can accomplish this by viewing the overall actions of each player, analyse them and develop a well-focused training plan to improve the performance. 

 

 

So, how do you read a radar chart? 

While plotting a radar chart is one story, reading the chart is another. The concept here is to plot a value along each axis and then connect those points to form a shape. 

To read the chart, begin with identifying the category each axis represents. This is followed by evaluating how the categories are related to one another. 

While reading the chart, you must consider a few aspects, such as :

  • The zero of each axis is considered as the centre of the wheel. 

  • The greater a point reaches towards the edge of the spoke, the higher the quantity. 

 

Radar charts are considered to be one of the most effective tools to compare a value with that of standard value. Although it is quite difficult to read this chart, the potential use of this chart is justified by many researchers. 

Some of the pros of using this spider chart are:

  1. Provide visual & vivid data description

  2. Realisation of dynamic analysis

  3. Allows to assess the symmetry of values rather than mere comparison of their magnitudes

  4. Accommodates quantitative scale for data consisting of multiple measures

Advantages doesn’t come without disadvantages. Just like any other charts, this tool has a few limitations. 

  1. Comparison of charts becomes complicated with increase in number of ‘webs’ or variables

  2. Comparison of values across axes is quite complicated when variables have different measuring scales

  3. Area and shape of polygon changes depending on the position of the axes 

A radar chart is perhaps one of the ‘love it’ or ‘hate it’ tool. This is because it creates a complex situation while working with some data, on the other data it works smoothly with some other data. The trick here is to use it only on suitable task and get the most out of it. 

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