Event selection for the straight line diagram
When creating a straight line diagram, you must specify which event layers you want to include in the straight line diagram and the order in which you want them to appear. By default, this list is automatically populated from two sources—the event layers that are currently displayed in your map document and any events that appear in your template. You can choose which of these events that you want included in the straight line diagram by checking or unchecking the check box next to the layer name. If an event layer does not appear in the list, you can click the Add button to add it to the list. You can also change the order in which the events appear by moving them up or down.
In the list, there is always an item called Reference Layer. Its check box is always checked and cannot be changed. The reference layer is a line that is created by default in the diagram without any events on it. The reference layer can be used multiple ways. For example, in the graphic below, the reference layer is used to symbolize the location where other routes intersect the route that is the focus of the current diagram. At the bottom of the graphic, you see that hatching has been used to display measures along the route. You can choose to display events above and\or below this reference layer.