Displaying terrain edges grouped with a unique symbol

Steps:

1. Right-click the terrain layer in the table of contents and select Properties.
2. Click the Symbology tab.
3. Uncheck Elevation (or any other face renderer that is checked).
4. Click Add.
5. Click Edge type grouped with unique symbol.
6. Click Add.
7. Click Dismiss.
8. Click Edge types in the Layer Properties dialog box.

By default, only the type 1 and 2 (soft and hard) edges are displayed.

9. Click Add All Values .
10. Click OK

Note:

You can display all terrain dataset triangle edges with the same symbol by selecting the Edges with the same symbol symbology renderer instead of the Edge type grouped with unique symbol symbology renderer. Also you can add and remove individual edge types from the display using the Add Values and Remove Values buttons.