When a line graph is the right choice?
There is one universal rule within data visualization; you should not use a visual just because it looks good overall. The visualization should always be selected for a reason, and it should answer a question about the data. Our Data Analyst and BI Book’s Product Owner, Valtteri Nättiaho, tells more about how to use the line graph properly.
The line graph is perhaps the most used graph style, and for a good reason. The line graph is excellent at showing changes over time, whether it is over a large or short period. However, I have seen cases where this evergreen graph style is misused due to its popularity.
The line graphs can be used to compare values over periods, but this does not mean it is always suitable to use for comparisons. One relatively common pitfall is to use the line graph to compare values over different categories but within the same period. For example, the graph below depicts fruit sales for January.
The sales for different fruits differ only by 0,1, but the initial impression of the graph does not reflect this. Additionally, the graph raises more questions than it answers. An example question would be what time period this graph is depicting. Instead of using a line graph in this case, we can use a traditional table visual. This way, the difference in sales is clear.