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Comment by nostromo | Hacker News Reader

I agree with the problem but disagree with the solution. I'd much prefer removing the stack completely and using overlapping plots, like this:

http://i.imgur.com/zO7CuQG.png

In a chart like this no data is lost in presentation. You can easily answer questions like "when did Android overtake iOS in marketshare?" and "is Windows Phone marketshare growing or shrinking?"

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Exactly. Stacked charts in general are misleading because they imply volume as a metric to be evaluated, when in any sort of number-over-time chart, volume is the last thing you need people concentrating on.

Unless it is a mekko chart in which case the volume conclusion is totally apt.

I wasn't aware of Marimekko charts[1] (well, not by that name anyway) before reading your comment -- but are they commonly used with a time axis? In the examples in [1] they seem like a pretty straight forward visualization of volume?

Off the top of my head I can't think of an example where a time axis wouldn't normally be used to visualize variation over time...? Perhaps quarter earnings as contributing to yearly earnings?

[1] http://www.fusioncharts.com/chart-primers/marimekko-chart/?M...

I've seen Mekko charts, or modified "mekko-ized" waterfall bar charts used with time axes. Blame management consulting.

One problem with overlapping plots here is that it doesn't convey that we are dealing with parts of a whole. Both the stacked area chart and stacked column chart naturally relate the growth of one component to the shrinking of another.

Relative comparison between slices of the stacked area or column chart is a difficult cognitive function, however, and is imprecise. I'd have to disagree with the article's author on the value of the stacked bar chart, as, while the step changes are more discrete, point-to-point comparison is still encumbered. The even more un-sexy clustered bar chart is yet more appropriate.

A solution, when the designer needs or wants to reflect total volume of that whole, is to underlay the lines (in this case) with an area plot representing the total volume over the same time interval. In this way, the two pieces of information (individual performance and total size) are encoded in distinct and easily understandable ways.

This pattern is good only when you effectively compare 2 variables; you easily see that when one shrinks, other grows, and when does it happen. When you have more variables, it automatically becomes too complex.

I don't like percentage plots. If one thing goes up by 1 point, then the rest must necessarily go down by 1 point (distributed between them). I think that's a bit confusing. I'd much prefer absolute values.

[PDF] http://sohcahtoa.org.uk/pages/files/fredas-tea-stall-three-c...

4 small groups of students (pairs or triples) repeated enough times to cover whole class. Each group gets one of these three charts or the table. Plenary at end: the ones who got the % bar chart often have totally different sentences from the other three groups.

I tend to give the % bar chart to the more confident students.

Personally, show me the numbers. Wins every time.

Isn't that exactly how it's supposed to work?

Yes, but human being seem to struggle with the concept, regularly assuming that a decreasing percentage necessarily implies a decreasing absolute number as well.

If they aim is to communicate a true representation of reality then you need to take that into account.

Consider that (unless the absolute value varies by more than an order of magnitude) you can see relative values very easily on an absolute graph, but you can never see absolute values on a percentage graph. It would be interesting to know, for example if the loser is still growing due to getting a smaller portion of an increasing market.

There are situations like survey research where percentages matter a lot and absolute values not so much.

Definitely agree with this. I don't design a lot of charts but I look at a lot of them and traditional line / bar graph charts are just so much easier to read and understand.

A lot of these new 3d type charts just come off looking like a flat 2d chart with layers and end up confusing the heck out of me.

I agree. The presented solution mitigates one of the problems, but does nothing to help you compare one of the sandwiched stacks over time.

Stacked charts are not very good at presenting information where there are more than two entities. Overlapping line charts do a much better job of presenting trends over time.

One of the other problem is when you have more then 5+ line, it becomes really hard to track the different lines. I have found out that a possible workaround is to show the path data on mouseover:

http://muyueh.com/see/nuk/efficiency.html (Better turn down the sound)

Using the button group in the left, you can zoom to different scale.

I can still see an advantage in stacked charts when a key piece of information is a sum of components. In the example on site, the data seems to be a proportion, and so there's really no purpose to stacking the lines because the sum is constant.

One could still depict totals as separate lines on a stacked chart, but for subset sums, a stacked area chart helps show how the sum is composed.

Unless you are color blind.

The chart in the linked example uses circles for all the markers. Giving each series a different marker shape (circles, squares, triangles, etc.) might help differentiate between them. Also, aren't there choices of colors that maximize readability for color blind people (as in the chart shown here[1])?

[1] https://en.wikipedia.org/wiki/Color_blindness#Design_implica...

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