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The two data visualizations in the article are poorly designed. They show line graphs where the X-axis is the type of EC2 instance and the Y-axis is the price.

The two data visualizations in the article are poorly designed. They show line graphs where the X-axis is the type of EC2 instance and the Y-axis is the price. Firstly, the X-axis of any line graph should be time. Or perhaps some other variable that "progresses". It's bizarre to use a category to label the X-axis of a line graph. Secondly, the X-axis is not ordered alphabetically, but seemingly randomly. I don't mean to be harsh, but a better data visualization would be a bar chart, not a line graph. Bar charts are better suited for categorical dimensions. Also, the type of EC2 instances should be grouped and/or sorted, but not randomized. This way, the information from the data visualization can be parsed more quickly and easily.

kqr 4y ago
The point at which you turn a bar chart or scatterplot into a line chart is when and only when intermediary values can be linearly interpolated between adjacent values. This is often the case when the X axis is time, but far from always, and there are other types of X axis that satisfies that property too. That's the strict way of looking at it. Slightly more loosely speaking, a line also helps comparing whether adjacent values are higher or lower, because humans are fairly good at judging angles relative to each other. So under this looser requirement, the X axis values have to be such that adjacent ones are more comparable than further apart ones. Under the looser requirement, time is actually a surprisingly bad X axis because values further apart are normally just as valid comparisons as those close together! There's a third, very loose reason to connect the points of a scatterplot with lines: it helps the eye judge the sequence of points, and thus get a sense of the internal variation in the series. This is a very loose requirement, but also a powerful tool.

kqr 4y ago

The point at which you turn a bar chart or scatterplot into a line chart is when and only when intermediary values can be linearly interpolated between adjacent values. This is often the case when the X axis is time, but far from always, and there are other types of X axis that satisfies that property too. That's the strict way of looking at it. Slightly more loosely speaking, a line also helps comparing whether adjacent values are higher or lower, because humans are fairly good at judging angles relative to each other. So under this looser requirement, the X axis values have to be such that adjacent ones are more comparable than further apart ones. Under the looser requirement, time is actually a surprisingly bad X axis because values further apart are normally just as valid comparisons as those close together! There's a third, very loose reason to connect the points of a scatterplot with lines: it helps the eye judge the sequence of points, and thus get a sense of the internal variation in the series. This is a very loose requirement, but also a powerful tool.