Necessity of y-axis label on a line graph?

I'm currently designing a line graph to provide a relative, "quick-glance" view of data trends, rather than the granular stock-market-style view. There will only be one trend line.

Currently each of the data points will be labeled with their y-values. The x-value will be linear units of time.

If the maximum y-value data point will be aligned with the top of the graph, is it okay to only show the x-axis label on the bottom?

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Could you show some mockups? – Sebastian Negraszus Jun 30 '13 at 18:21
Of course – updated. – ewittke Jun 30 '13 at 18:55
For starters, what unit is the y-axis in? You need to show that somewhere. And if you show it with a label on each node, then it might get messy. FYI if you are going to label each and every node, I'd not make this a line graph but instead just plot each point out rather than connecting them. – DA01 Jul 1 '13 at 2:33
Will the bottom of the chart be always 0, or might it fluctuate? – André Jul 1 '13 at 7:21
@André: The bottom will always be 0. – ewittke Jul 1 '13 at 14:46

For "quick-glance" it is okay not only hide y-axis but also hide x-axis. An example are sparklines, although they fit more as inline graphics.

The reduced version of a trend line is just an arrow. It is perceived really fast and any axes make it look complex.

One thing you should consider is to use such graph in strong context as supplementary material so the users could understand graph.

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There are a few questions you need to ask before removing the axis.

• Is the user familiar enough with the content of the graph that he will never have to second guess what the content is? eg: Since I have no idea regarding the context of the graph, it took me a while to figure out what it is about.

• Is this the only graph in view? If so, I would keep the axis. Like Alexey pointed out, there are cases where you want to remove the axis for the sake of better legibility and usability, like with the sparklines or maybe in large set of small multiples

• Finally, what value are you getting by removing the axis? Are you getting some additional space? Are you making the overall readability of the site/product better? If there is no concrete and strong answer to this, I would look for some different axis designs but not remove them completely.

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These are good things to think about. It seems that the clarity of keeping the axis outweighs the minimalism of removing it. – ewittke Jul 1 '13 at 14:43

I think it partly depends on how many observations you'll have. For 7 days I'd recommend a column chart instead of a line chart. To me, it looks like something is missing without the Y-axis.

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See this depends on the usecase: For an alert type service, using sparklines, there is no need for axis. Also now in graphs like d3.js etc, we can show points to hover and this will display the value, but note this way the use has to manually go and hover so -1 on usability. Hence axis come into picture for quick visualization. I would say it depends on the dataset and view(size of the chart)

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• I am in the business intelligence field so I make and see charts every day. I have seen line charts and I have even seen sparklines, but I rarely see a chart that has an X-axis but no Y-axis.
• Is it important to show the datapoint labels on the chart? If your users are mostly only interested in the overall trend, the labels can become visual noise to the users. You can show them as hover over tooltip instead.
• If you want to remove the Y-axis, you should also remove the Y gridlines since they add no value to the chart.
• Consider also removing the tick marks on the X-axis.
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It's okay to use axis-less graphs when you are just trying to hint at values/trend.

It also okay for them to be smaller. In fact, some of the time, making them smaller seems to make the trend more obvious overall.

Also, tooltips allow you to minimize contextual information in the graph, if you are looking to simplify a more detailed graph.

Take a look at this Google Analytics example:

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