Properly display multi-line chart when series overlap

Question

I am working on a report that requires a multi-line chart (representing how a given value varies over time among different groups) They are displayed in a single chart sharing both axis. My problem is that at some stages, the data looks similar to this:

    DAY:  1   2   3   4
GROUP A: 10  12  15  18
GROUP B: 11  12  15  20

Now, the lines joining days 2 and 3 will overlap with each other, so the one that is drawn later erases the previous line. I've thought of a few solutions, not all of them entirely convincing:

• Color mixing: let's say I draw the series for group A in red and the one for group B in yellow. I would draw the overlapping section in orange.
• Randomization: adding a small random value to each point, big enough to make the lines distinct, but small enough to keep the "fake data" as close to the original as possible.
• Layers: making the first line slightly thicker, so that when the second line is drawn on top, it doesn't completely disappear.

In my real problem, I sometimes have 3 or even 4 overlapping lines at some sections, and each line has about 20 points. I would like to know if there are other more interesting solutions (or at least, which of the ones I thought of you would recommend as a "best practice")

This is an example of one of those charts (in its pure form, without any correction)

Here the "randomized" chart:

Answer 1

This happens alot with charts and honestly there's nothing wrong with overlapping values, people will get it when some values are identical. However, some ideas to fix this:

• use a bar chart (if possible with your data)
• use filled shapes instead of just simple lines (if possible with your data)
• use multiply on the top line, so when overlapping, it automatically changes color

Answer 2

Just made some tests. 3D looking graphs are difficult to read when there are many days and groups. I recommend you to use conventional spreadsheet style graphs. Here's an example in LibreOffice Calc (=freeware):

Creating these needs only few clicks. There's a column graph and a line chart with dots. Both of them present the same data.

The graphs can be exported as vector for ex. by copying and pasting them to Illustrator or other drawing program. Here one chart is pasted to Inkscape and the coordinate lines are colored and made thicker:

The numbers are still text objects. The graph lines are unfortunately colored rectangles, so they should get the final thickness in the spreadsheet.