In a trace network, understanding how resources flow along a network edge is essential when performing traces. The direction of flow in the trace network is managed through a system-maintained network attribute named Flow direction. When a trace network is created or converted from a geometric network, the Flow direction network attribute is added to all line feature classes that participate in the network.
Set and display flow direction
When the trace network is created, the direction of flow is set with the digitized direction of the line for all features in line feature classes that participate in the network. Edits made to the values in the FLOWDIRECTION field determine the direction of flow. Flow can be specified as indeterminate, with digitized direction, or against digitized direction.
Trace Network Version 1 requires the use of the Set Flow Direction tool to update the flow direction of line features in the network. The trace network can be upgraded to Trace Network Version 2 or later to use the Flow direction network attribute and associated workflows. See Trace network upgrade history for more information.
The Display Flow Direction command on the trace network's Data tab allows you to visualize the flow of resources in your network through a layer that displays flow arrows for network line features in the current extent of the active map.
Work with flow direction
Tracing analytics rely on the flow direction set in the FLOWDIRECTION field to determine directionality in traces. Changes to the flow direction of a line impact the results of upstream, downstream, and shortest path traces. If changes are made to the Flow direction network attribute, a dirty area is generated to mark the feature for validation. Validation ensures that the flow direction is updated in network topology. Once updated, the Display Flow Direction command can be executed again to display the updated direction of flow.
Disabling a network topology is recommended when updating the flow direction for a large number of features, as this prevents the need to create and validate dirty areas. Any changes made to the flow direction of a feature class while the network topology is disabled will be validated during the enable process.