All You Need to Know to Build Radial Charts in Tableau
Radial Charts have always intimidated me because I considered them difficult – probably because all the tutorials I came across mentioned copying and pasting a few calculations without any logical explanations. Am I supposed to look it up every time I am in need of a radial chart?!
Well, luckily I am not a copy-paste person. I can remember things only when I understand them, and I like to grasp the concepts behind what I'm doing. So, I tried creating a radial chart while understanding the logic behind various steps involved, and it was like magic unfolding in front of me. So, let's get to it!
Please note that for this article,
- All images, unless otherwise noted, are by the author.
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The dataset used is : The Sample – Superstore data set. It is a free dataset which comes with Tableau. It contains information about products, sales, profits, and so on that we can use to identify key areas for improvement within this fictitious company.
We will start by understanding how to plot data on a circle. We will then implement the same principle to create two different types of radial bar charts.
First, some basics, please!
From school geometry, recall what we know about circles.
A circle is a two-dimensional figure consisting of all points equidistant from a given point. The given point is called the center and the distance is called the radius.
To plot a radial chart, we would need a radius and a centre.
Let's assume, for simplicity, that we have only twelve data points. To plot these, we need :
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Radius(r): Radius can be any arbitrary number depending on how big you would like the radial chart to be. For our purpose, let's assume it to be 1.
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Angle(θ): Find a round watch/clock. Notice how all the numbers are spaced at a uniform distance. In a circular watch, there are 12 numbers located at 30° each(12 X 30°=360°). We also need our points to be located uniformly across the circumference. To achieve this, just divide 360 by the number of points to get the angle between them.
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Co-ordinates ( x,y): How do we map these twelve data points to the circumference? Recall the basic trigonometry formulas for cos(θ) and sin(θ) for a right-angled triangle :
cos(θ) = Base/Hypotenuse
sin(θ) = Perpendicular/Hypotenuse.
If we consider the radius to be the hypotenuse of a right triangle, then cos(θ) gives us x, and sin(θ) gives us the y-coordinate, since we are assuming radius is 1.
Now, in order to map the data points on a circle, we would need respective x, y co-ordinates for all the twelve data points.
Basic Radial Chart
A basic radial chart can be built in just three steps:
- Calculate Angle(θ):
Total(count(Point))gives the total number of points available in data set. In our case, it is 12. If you consider the Sample Superstore dataset, this point field can be region or city or basically any dimension. Dividing 360° in 12 equal parts gives the angle(
