alt Hacker NewsWhile it is generally considered a No-No to start a bar chart from a baseline that is not zero, there is no corresponding prohibition, especially among numerically sophisticated audiences, for scatter plots or line charts. In general, we want graphs to focus on the area of variation.
For example, take a look at just about any stock chart (try https://www.google.com/finance/beta/quote/GOOG:NASDAQ?hl=en). There's actual money on the line, but no baseline. Why do you think that is?
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For stock prices, starting the y axis wherever is aesthetically pleasing makes some sense because everybody will have a different non-zero cost basis for their investment, and the graphs need to be able to clearly depict fluctuations that are minor on a percentage basis. For something like the em-dash prevalence on HN, the most meaningful question is whether it has doubled, tripled, or whatever relative to the pre-LLM corpus, and that's most clearly visually depicted by starting the y axis at precisely zero.
> In general, we want graphs to focus on the area of variation.
Visually, this is vastly exaggerating the variation. Actual usage did not even double.
> take a look at just about any stock chart
Honestly, I hate that about stock charts. They adjust the axes and scales so that the graph itself provides no information. Did it go up 1 point? 200 points? 5%? 50%? You can’t tell, because the graph is just a scale free squiggle.
The real answer actually depends. In cases where you want to visually emphasize the ratio between any pair of values, you should start from zero. In cases where only the difference between any pair of values matters and the ratio is meaningless you can start at a different baseline. A surprising number of measures are interesting in their ratio though, so we generally prefer a zero-based chart.