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A bubble chart tip you may never have noticed: How to let colors and shapes reveal more information?
The bubble chart is a graph that displays three data dimensions. Each entity has a set of associated data for triples (v1, v2, v3) and is depicted in the form of a disc whose position represents the first two values and the third value is presented in size. Bubble charts help understand social, economic, medical and other scientific relationships. They can actually be regarded as a variant of scatter plots, while data points are replaced by bubbles. According to Microsoft Office documents, bubble charts can be used to visualize data. If the data contains three data sequences, each with a set of values, the size of the bubble is determined by the value of the third data sequence.
"You can use bubble charts instead of scatter plots, if your data has three data series, each containing a set of values."
Select bubble size correctly
Using bubbles to represent pure quantity (single-dimensional) values can be misleading. Human visual systems usually perceive the size of the disc based on their diameter, not the area. This is why most chart software requires that the bubble size used as the third data value be expressed in radius or diameter, rather than area. A misleading scale setting can lead to extreme misunderstandings, especially when the data is wide. Therefore, the bubble chart needs not only to be properly scaled, but also to clearly mark to indicate that it is the area rather than the radius or diameter to convey the data.
"Judgement based on bubble size can be a problem, whether it is the area of use or the diameter."
Show zero or negative data values in bubble chart
The way in which the metaphor of data values is expressed as disk area cannot be extended to display negative or zero values. Some bubble chart users will turn to graphic symbols to express non-positive data values. For example, the data v < 0 can be represented by a disk with an area of v, and the symbol "×" is placed on the disk to indicate the size of the bubble to indicate the absolute value of the negative number. This method is relatively effective when the size (absolute value) of the data value itself is relatively important.
"For zero-value data, some users simply do not use discs, but use other graphics such as squares."
Integrate more data dimensions
In addition to the three main values, additional information about the entity can be presented through systematic colors and patterns. At the same time, supplementary information can also be added by labeling text on the disc, which can be simple unique identification tags for cross-reference interpretation keys, etc.
Other uses
In architecture, the term "bubble drawing" is also used in the first phase of architectural sketches, which are composed of bubbles. In software engineering, a "bubble graph" can refer to a data stream, data structure, or other graphs represented by circles or bubbles, and are represented by links. In information visualization, the bubble chart may indicate that the digital quantity is represented by tightly packed circles whose areas are proportional to the quantity. Unlike traditional bubble charts, this graph does not give any meaning to the x-axis or y-axis position, but instead attempts to wrap the circles tightly to make use of the space efficiently. This bubble chart was first introduced by Fernanda Viegas and Martin Wattenberg and quickly became a popular method for displaying data, with circular package charts also included in popular visualization kits such as D3.
In daily life, bubble charts may change your understanding of data and allow you to explore the stories hidden behind the data more deeply, but have you ever thought about how such visual presentation will affect your decision-making judgments?
