What is the criterion for adding a trendline to your visualization?

A trendline is a valuable analytical tool used in visualizations to help identify patterns or trends in data over time. To add a trendline effectively, it is essential that the visualization includes a period column—this is a time-related variable such as dates, months, or years.

Having a period column on one of the axes allows the trendline to correlate changes in the data with specific time intervals. A trendline illustrates how the data points behave over time, revealing whether there are upward trends, downward trends, or stability during a certain period. This temporal aspect is a fundamental requirement because it enables the viewer to interpret the data in the context of timing, which is crucial for understanding market dynamics, seasonal effects, or other time-related changes.

In contrast, if the visualization lacks a period column, it would not be meaningful to apply a trendline, as you wouldn't be able to associate the changes in data with a time variable. This condition is why having a period column on one of the axes is key to justifying the addition of a trendline to a visualization.