Trends are often connected to time. **Heat maps** (see [Part-to-whole charts](Part-to-whole%20charts.md)) can be used to visualize the patterns and correlations across several categorical variables (on the Y axis) over time intervals (using hour, day, month, year, etc. on the X axis).  An **Alluvial diagram** can also focuses on change over time, thereby depicting (specific) trends (especially, in interactive versions). Note that often there is a confusion and Alluvial diagrams sometimes erroneously get called *Sankey charts* (see [Visualize flow](Visualize%20flow.md)).  The **Horizon graph** can be used to compare the trends across many variables at the same time. It is particularly useful when you have a line plot with too many lines that makes it hard to read the trend for each of them.