You can change the symbology of features by adding geometric effects to representation rules. Adding geometric effects does not alter the underlying geometry of the features.

In this example you'll see how to edit a representation rule to convert a single stroke line symbol to a pair of strokes offset on either side of the original line.

To do so, open the layer properties for the line (in this example, TrailL_Rep). Click the representation rule (in this example it is called Trail) and click the stroke symbol layer. Click the (+) button to see the Geometric Effects dialog box. Click Line input, then click Offset curve. Click OK on the Geometric Effects dialog box to add a new dialog box to the stroke symbol layer, labeled Offset curve. In the Offset text box, type “0.5” to specify how far from the original line this stroke will be offset.

Next, add a new stroke layer to this representation rule by clicking the Add New Stroke Layer button. The newly added stroke layer has a line width of 1. This is the default value for new stroke layers. To reduce the width of the line, type “0.5” in the Width text box.

Next, click the new stroke symbol layer. Click the (+) button to see the Geometric Effects dialog box. Click Line input, then click Offset curve. Click OK on the Geometric Effects dialog box to add a new dialog box to the stroke symbol layer, labeled Offset curve. In the Offset text box, type “-0.5” to specify how far from the original line this stroke will be offset. The negative offset puts this stroke on the other side of the original line.