In this example you will see how to create symbology for a situation in which you have information about the location for tunnels but no data to actually represent the tunnels. You know from some fields in your feature classes that you have roads and railroads crossing above and below each other. This information tells you that at those locations where two features intersect each other, one feature crosses above the other. For your maps, you want to use this information to create tunnel symbology.

The Create Underpass tool performs this complicated operation. This tool is located in the Symbolization Refinement toolset. There are several parameters on this tool; some are required, and others are optional.

When the tool is complete, you will be able to symbolize your features in a way that clearly indicates one feature is crossing under the other. This is done using masks to hide one feature and a new linear feature class that provides the tunnel symbol.

You can indicate which features are under other features by setting the first two parameters.

To do so, open the Create Underpass tool. Choose RoadL layer.lyr for Input Above Features With Representations and RailroadL layer.lyr for Input Below Features With Representations. Type “2” for Margin Along and type “1” for Margin Across, then choose Points for both from the drop-down lists for the unit of measurement. Following this, you will select your own locations for the mask feature class (Output Underpass Feature Class) and mask relationship class (Output Mask Relationship Class). Type “Under_FC” and “Under_RC” for the names of the new feature class and relationship class.

Next you will see the tool’s optional parameters. Without these parameters, the tool will complete as expected and create the masks you need to indicate which features cross over others, but it will only create the minimum required parts for underpass symbology. These optional parameters allow you to indicate how you want the underpass to look.

You can choose to enter a SQL expression to refine your selection. Without a SQL expression, the tool will process every feature in your feature class. Although there is nothing inherently wrong with this approach, it will take longer for the tool to complete. In this tutorial, the tool will complete in less than 30 seconds. Your computer speed may vary, so the elapsed time could be as long as two minutes.

For example, you may want to place a tunnel at every location where a road crosses a railroad, or your data might not have an attribute field on which to make a refinement selection to make the tool process on a smaller set of data. As shown earlier, a data field indicates where a crossing occurs.

Click the SQL button to open the Query Builder dialog box. On the Query Builder dialog box, double-click RelationshiptoSurface to add it to the SQL expression box, click the = button to add it to the SQL expression box, click Get Unique Values, then double-click the 3 entry to add it to the SQL expression box. Click OK to close the Query Builder dialog box.

Type “Tunnel_FC” for the name of this new feature class. Choose PARALLEL from the drop-down list to indicate the wing type you want to use. Type “1” and choose Points from the drop-down list to indicate the length of the wing ticks for your tunnel symbol.

Click OK to run the tool.

When the tool finishes running you will have created two new feature classes and a relationship class to use in your map to display tunnels. The mask will be linked to RailroadL with the relationship class.