A starting point is set on network features to define the location in the network where a trace begins. Most traces require one or more starting points to be defined.
You can create and manage starting points, specify terminals, differentiate between coincident features, and set multiple starting points using the Starting Points tab in the Trace pane.
Keep the following in mind when working with starting points:
- For a starting point to be valid, the network feature it is placed on must exist in the network topology. Ensure that network features used for starting points have been validated.
- When working with spatial features on the map, a coincident point is created on the map to denote the starting location for the trace. You can also select records from the nonspatial edge and junction object tables and add them to the Trace pane to serve as starting points:
- For points, devices with terminals require that you specify a terminal to set as the starting point.
- For lines, a starting point can be placed anywhere along the line feature.
- For polygons, the starting point is placed at the centroid to mark the starting location.
- For junction objects, features with terminals require that you specify a terminal to set as the starting point.
- For edge objects, a starting point is placed on the object to specify the starting location.
- By default, starting points are placed with a percent along value of 0.5. This can be modified by editing the PERCENTALONG field for the starting point in the UN_Temp_Starting_Points feature class.
- For subnetwork-based traces, the starting points must reside in the input tier.
- If the Subnetwork Name parameter value is specified for the Trace tool when performing a subnetwork trace, starting points are not used. The trace begins at the subnetwork controllers instead.
- When using starting points on line features and edge objects, the trace results include the entire line feature, not
just from the portion of the midspan starting point.
Note:
By default, trace results are returned as a selection and include the entire line feature. When a starting point is placed midspan on a line, you can use the Aggregated Geometry option of the Result Types parameter to return partial feature results in an output multipart geometry feature class. When a starting point is placed along a line, trace results begin at the starting point location and can return partial feature geometry for the feature. When edge objects are content of a line feature, partial geometry can also be displayed for edge objects with midspan starting points in the aggregated geometry result using the Synthesize Geometries parameter.
When a starting point is established using the Trace pane, the UN_Temp_Starting_Points feature class is created in the project's default geodatabase. Successive starting points are appended to this class. To remove all starting points from a map, use the Clear All button 
on the Starting Points tab.
Starting points can also be specified in a user-defined feature class or created by using the Add Trace Locations tool. This tool creates an output feature class with the same schema as the UN_Temp_Starting_Points and allows selected spatial network features to be output to a user-defined feature class for use in a script or model.
When an existing user-defined feature class or table is used to supply starting points for the Trace tool, the following are requirements:
- The schema of the user-defined feature class or table must contain a FEATUREGLOBALID field of type guid similar to that found in the UN_Temp_Starting_Points feature class and contain a value for it to be applied to the corresponding network feature as a starting point.
- When this field is not populated, features without a corresponding value are not used to place a starting point.
- The schema of the user-defined feature class or table must contain a PERCENTALONG field of type double to place starting points along a line feature or edge object.
- The PERCENTALONG field must contain a value between 0.0 and 1.0 to indicate the location of the starting point along the edge.
- If the PERCENTALONG field is not present or does not contain an appropriate value, it is assumed the starting point is to be placed on a junction, and placement along an edge is ignored.
- The schema of the user-defined feature class or table must contain a TERMINALID field of type long to place starting points on a junction feature or junction object.
- If the TERMINALID field is not present or does not contain an appropriate value, it is assumed the starting point is to be placed on an edge feature, and placement on a junction is ignored.
- When working with a utility network version 7 or later, the schema of the user-defined feature class or table must contain a FEATUREOID field of type Big integer and a 64-bit OBJECTID field. The object ID field can be migrated to 64-bit using the Migrate Object ID To 64 Bit tool.
Learn more about how to set starting points and barriers