A flag marker represents something that occurred at an instant in time in an app. A flag can represent many kinds of application events. For example, a flag could show when a particular work item was scheduled or when an exception was thrown. Runtimes such as the Task Parallel Library can also generate flags.
Sometimes flags occur so close to one another in the Concurrency Visualizer that they can’t be drawn individually. When this occurs, a gray aggregation flag that represents the underlying flags is shown. When you rest the pointer on one of these icons, a tooltip displays the number of underlying flags that are represented. To view the flags, zoom in. If you zoom in all the way and still get an aggregation flag, you can view the underlying flags in the Markers Report.
Aggregation flags are drawn in different sizes. The size depends on the importance level of the most important flag in the aggregation. The following illustration shows aggregation flags in increasing order of importance.