I need to demonstrate that move people spend more time checking their e-mail at certain times of day than others. So I created this chart:

enter image description here

I thought it was this was apparent, but it proved too much work to understand. Instead I am trying out designing this clock, which seems even less intuitive.

enter image description here

What is a good chart for describing dependence on time of day?

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    Are you trying to demonstrate the frequency of email checking throughout the day (24 hours)? Your chart contains the line graph (blue line), which I understand, and area graph (light-blue area) which is confusing and I'm not sure what it means. Also, if you label your chart's x and y axis, it would be much easier to understand. – Chairman Meow Jul 17 '14 at 23:41
  • Not saying that this is how you should do it, but there is an interesting post on bitrebels.com/social/… that you might get some inspirations from. – Michael Lai Jul 17 '14 at 23:47

Keep it simple, and as conventional as possible. Rectangular charts are the most common. Label the axes and pay attention to typography. Maybe use military time. Maybe emphasize (darken) the hour lines on the points of the clock (12, 3, 6, 9...).

There's tons of existing charts of this nature out there, I'd spend some time exploring them to glean some ideas.

charting hours of day examples

charting hours of day examples data visualization

And remember Tufte's basic rule of information display, which is to not use any ink that doesn't impart information.

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  • For similar charts I've had people stumble over fractional units because they do not understand it is an average. Also I have had to explain the error bars to many people - although I definitely think they should be included. – Andy W Jul 18 '14 at 12:25

The first problem is to show the course of a single day in a form the reader can easily grasp; the second is to relate your data series to this picture. Although "time of day" is a simple one-dimensional parameter, we associate a structure with it (workday, evening, lunchtime etc.) which can cause a certain dissonance when we see it plotted in linear form as in the first example.

(That said, if your audience can't understand that graph, then you have your work cut out for you...)

One thing that might help is simply to distinguish day from night:

enter image description here

This might seem like spurious decoration, but I'd argue that it helps the reader align the graph with their mental model of "a day"-- they can quickly see that the numbers are higher at lunchtime and in the afternoon, and at a minimum in the small hours of the morning, without having to constantly refer to the axis labels.

I left out the area graph (error bars?) because by being there it demands an explanation, and that explanation is much harder for less-numerate people than a simple line graph. It doesn't seem that important anyway, since this graph is more about the trend over time than the specific y-values. I omitted the horizontal gridlines for the same reason.

Of course, another way to represent time graphically is to use actual time:

enter image description here

This sketch example could use a lot of improvement, but you probably get the basic idea: one whole day is presented as a speeded-up "video" of the data series. In theory it doesn't require any graph-literacy at all; if you can understand a time-lapse video and read a thermometer, you should be able to figure out such an animation. On a 5-second loop like this, it's even feasible to read actual values off the graph.

The animation frames could also be displayed statically in "comic strip" form; this would be a simple example of a pattern referred to by Tufte as "small multiples" (Tufte E. Envisioning Information, Graphics Press 1990).

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