When tracing line or polygon features, you may want to add vertices as you move the mouse rather than clicking each time you want to add a vertex. Stream mode digitizing lets you do this.

Before starting to digitize in stream mode, you need to set a stream tolerance—the interval at which the sketch adds vertices along the feature you are digitizing. The default tolerance value is 0 map units, so if you don’t enter a tolerance value, you may find vertices that overlap each other.

You will also need to specify the group tolerance—the number of streaming vertices you want to group together. The number you set tells ArcMap how many vertices to delete when you click the Undo button. For example, if you set this number to 20 and click the Undo button while you’re digitizing a feature, ArcMap deletes the last 20 digitized vertices from your feature.