Line charts are great to visualize trend over time. I use line chart extensively in my reports to show traffic, conversions or leads over the past year, 13 months, etc.
While they are very effective to show how certain values increase or decrease, line charts have limitations when it comes to the number of categories (lines) we are trying to visualize. If we stuff more than three categories into a line chart to compare values for these categories over time the chart becomes totally ineffective, difficult to read and impossible to draw insights from.
Here is an example.
This line charts compares multiple years for website traffic. I personally don’t see much value in comparing website traffic for the past 5,6 or 7 years but I am being asked by clients to go back this far and even further.
If the insights you are looking for lie on data that goes that far back in time, there is an option to visualize it with the following chart
This is an area chart but you could use a simple line chart too. If you do have such large set of data there isn’t really a perfect solution. As the above area chart will still require a bit of work from your audience to look at let’s say June this year vs last year vs previous years. However this visual makes way easier to follow a pattern and quickly identify gains or losses and then spend more time investigating.
Another example where I have seen the use of multiple categories in a line chart in digital marketing reports is visualizing website traffic trends by marketing channel.
Like this example.
Even if there are insights to be taken from this set of data, they are not easily identified with a chart like this.
Here are a couple of alternatives:
Separate line charts for each marketing channel
A short dashboard with a line chart for overall website traffic trend and charts to compare website traffic by channel vs previous month and vs this month last year.
Watch my short webinar on how to avoid having multiple lines in one chart
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