What type of visualization is best used to show trends over time?

Line charts are the most effective visualization for showing trends over time because they illustrate data points in a sequence and connect them with lines, making it easy to observe changes and patterns across different time intervals. This connected representation highlights the continuity and direction of data, allowing users to see upward or downward trends clearly.

In contrast, bar charts are more suited for comparing discrete categories rather than depicting how values evolve over time. Pie charts are useful for showing parts of a whole at a specific point in time but do not convey trends. Scatter plots can demonstrate relationships between two variables but don't inherently represent changes or trends over time as effectively as line charts do. Thus, line charts are the optimal choice for trend analysis.