Labelling chart data granularity / interval

Question

If a line or bar chart is rendered as a part of a time-series, is it necessary to label somewhere around the chart what the granularity/interval of the data is?

Example:

I can see labeling the chart with the granularity being slightly useful. But does adding the label warrant adjusting the Data-Ink ratio to include it?

Answer 1

Some people argue that a chart should be unambiguous to the audience without having to specify the exact context, and to do that you would have to err on the side of caution and introduce perhaps more 'ink' than you would otherwise need to when the context is understood (or if there is already an existing convention).

So looking at the chart that you provided, I can see some opportunity to optimize the clarity of the information if you want to achieve the ability for the chart to be a stand-alone piece of information.

• Add a title to the chart that is meaningful (and can reduce the labeling required)
• Present both major and minor tick marks (if it is not too dense)
• Use interactive elements on the chart to introduce or reduce information when the section is not active or focused on
• Establish a standard or convention so you don't need to repeat certain bits of information or design when the context is clear

Answer 2

Everything depends on the use case — if people care how it changes hour-by-hour, it's useful. The "hourly data" label definitely helps understand that there are 24 data points in between every two points on the X axis.

Only thing I would change in the example is that I put the dates in between the points on the X axis and got rid of the timestamps entirely, like in the chart below:

Answer 3

I myself don't think so, since it is pretty clear from the x axis what the intervals are. However, if the labels will be organized better it wouldn't hurt, like so:

Tue, Dec 01

12:00 pm

and not:

Tue, Dec

01, 12:00

Answer 4

Another option would be to add a tooltip for the series, to provide further details of the corrected item.