When you have a table with 3 related dimensions of data, how do you represent it on a flat 2D chart? Put three column charts side by side, one for each dimension? Or use two XY-plot charts? But both of them will be ineffective in putting together all the 3 parameters in one elegant visualization. Time to say hello to the bubble chart.
What are bubble charts?
Bubble charts plot data defined in terms of three distinct numeric parameters. They allow the comparison of entities in terms of their relative positions with respect to each numeric axis and their size as well.
Column charts and line charts have 2 axes commonly – a numeric axis and a categorical axis. The Y-Axis is the numeric axis for column and line charts. This means that the quantitative magnitude of the plot is indicated by the position of the plot with respect to the Y-axis. Bubble charts are different because both axes of a bubble chart are numeric. Hence, the position of the plot is an indicator of two numeric values. The area of the plot is an indicator of the magnitude of the third numeric characteristic.
The bubble chart above is supposed to help you manage your investments in equities better. The X-axis and the Y-axis are used to denote Age of Investment and Return on Investment respectively. Apart from these 2 parameters, what is the third parameter that you would be interested in? Obviously, how much have you invested in a particular equity? So that is denoted by the area of the plot. Quite clearly, A has the largest RoI and the largest investment size as well.
But you could have made that out from the data table itself. How did the bubble chart help you? Since we have taken up a very basic example, only 5 investments have been shown. But in reality, the number of investments will be much higher. In that case, the bubble chart will help you form a mental visualization like this:
The same bubble chart has been divided into 4 quadrants. Depending on the parameters, each of the quadrants has a particular meaning for you.
- Quadrant 1 - Best investments: Investments that have given high RoI in a short period of time. What else could you ask for? These investments are like jackpots.
- Quadrant 2 - Good investments: Long Age of Investment but great RoI. If you are planning to make further investments, you would surely invest in the equities in this quadrant.
- Quadrant 3 - Not-so good investments: Low RoI over a long period of time. Further investment on equities in this quadrant would be your last bet.
- Quadrant 4 - Decent investments: Manageable RoI over a short span of time. If you are thinking short-term investment, then this is your quadrant.
With a larger number of data plots, mental divisions like this are very helpful in determining the next course of action.
Variants of the bubble chart
What we have discussed till now are single-series bubble charts. You can also have multiple series of data plotted in the bubble chart. The series will then have different colors with the legend pointing out which color refers to which data series.
In our Investments – Equities example, we can also show Mutual Funds in the same bubble chart.
Using bubble charts like this, you can see view all your investments at once. Then you can decide which investments you should pump more money in and which ones should you divest.
Where can bubble charts be used?
Apart from using bubble charts for investment, there are a whole lot of other places where bubble charts can be used. Some examples to stir up your imagination:
- To see if higher promotional expenses lead to more footfall and in turn to more revenue for a bunch of retail stores for a month: The X-Axis can have the average daily footfall, Y-Axis the promotional expenses and the area of the plot will show the revenue generated by the outlet for that month. This can help find out which store was able to promote itself successfully and whose promos failed.
- Checking if higher CPC leads to higher clicks and better conversions in PPC Campaigns: To check if your excess spending on increasing the CPC to get better ad positions are getting you more clicks and finally leading to more conversions, a bubble chart will be useful.
Go see more examples of the bubble chart here.