1. What is an error type chart?

Our monitoring system measures the parameters of telecommunications services at regular intervals, and based on the measured parameter values, automatically decides if there were service errors. For every monitored service, there is a chart on our dashboard, which displays in percents the ratio of error-detecting measurements to all measurements. Different service error types are displayed with different colors.

2. EASY CASE: Mutually exclusive error types

In most cases, one measurement can detect at most one service error type, so I could use stacked bar charts. This way the user can examine not just the percentage of different error types, but also the total percentage of errors, which is shown by the total height of the stack. Example chart with 6 possible error types:

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The users like this solution.

3. MY PROBLEM: Simultaneous error types

In rare cases one measurement can detect more than one service error type, even all of them.

a) I cannot use stacked bar charts because the height of the stack would be misleading. For example, if there are 100 measurements, and 5 of them detects errors, but all of them detect the same 3 error types, then the top of the stack would be at 15%, while the total error ratio is 5%.

b) I also cannot use use unstacked bar charts, because at the smallest supported display resolution there are only 10-15 pixels for every time interval, so there would be only 1-2 pixels per bar if I put them next to each other.

c) Both problems could be solved by unstacked line charts. Here is an example with 7 error types:

enter image description here

Unfortunately the users don't like it, because "it's very hard to see the total error percentage". Although there is another chart which displays the total error percentage, they would still prefer being able to see its value on the error type chart. I could add yet another, possibly thicker chart line, which shows the total error ratio but in some cases there are 16 different error types and I'm not sure that adding a 17th line with a special meaning wouldn't make the chart too complex.

4. MY QUESTION: How could I display on the same chart not just the different error type ratios, but also the total error ratio in a meaningful way?

  • My first instinct is that if there is too much information to interpret in the one chart, even if you managed to put all the information in there it will not be very user friendly. Would you consider something like a small multiple (en.wikipedia.org/wiki/Small_multiple)
    – Michael Lai
    Commented Jun 22, 2021 at 23:52

2 Answers 2


So, if I understand correctly, you need to display two types of information on the same graph: total error ratio and grouping of those errors by type.

The problem you have arises because you essentially try to encode two different types I see three solutions, maybe they can work, although it doesn't seem there is a perfect one:

  1. You could separate the info into two separate charts: one for total (percentage), one for types (count). Of course, there's an issue with additional space needed for additional chart. If the users can interact with the graphs (it looks like they can, as you're showing a cursor with tooltip details), you could make a switch (like a toggle or segmented control) in the graph slot, so the user can switch between the two in the same slot. If it's not interacted with (e.g., just stays there on the screen auto updating), you could make it so the chart switches automatically, alternating one chart with another every couple seconds in the same slot on the monitoring grid. There are some usability issues with that, but it all depends on the use cases.

  2. You could introduce not just error types, but also error type combinations as types. Say, error type "A" is red, error type "B" is blue, error type "A and B" is red and blue (like, gradients, or diagonal stripes, or even different colors (red + blue = purple 😃 ) for the overlapping types). This gets exponentially more chaotic the more types there are, as you'd have to introduce new color (or whichever type of encoding you choose) for every combination, but you could only show the types that are actually represented on current chart to make it a bit simpler.

  3. You could combine stacked bars with unstacked ones. As in, for every hour (or whatever does the X-axis represent) you'd have two columns - one for total percentage and another one - stacked, for different types. Just make sure you make the total column very distinct, like make it black or gray, so it is clear, that it's different from the stack. Although this option could get confusing, I'm sure with proper legend it could work.

  • 1
    My answers to your points: 1. As I wrote above, I have already created two charts, one for the total error % and another for the error types. 2. One of the users already suggested this, but as you wrote, this would lead to having too many colors and total chaos. 3. Interesting idea, I will think about it.
    – kol
    Commented Jun 29, 2021 at 9:05

A little difficult to understand and explain for someone who is outside the project. I can only write something generic as an answer.

Comparing elements in the same period leads to overlapping data, more or less what you explain in the last part.

There are overlap charts:

Overlapped Range Bar Chart

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Overlapped Bar Chart

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