Managing default schematic layer properties
Schematic layer properties can be specified in ArcMap for each opened diagram and can be very different for each diagram. But since a diagram template is dedicated to a particular type of schematic diagram, it's usually better to get the same layer properties for all the schematic diagrams based on the same diagram template. Default schematic layer properties are the set of schematic layer properties specified at the schematic diagram template level that allows all schematic diagrams based on that diagram template to be displayed in the exact same way.
Default schematic layer properties are specified using the Schematic Dataset Editor at the diagram template level.