For the network algorithms to process correctly all polylines must point in a source to sea direction. Polylines labelled zero from Strahler ordering or recognised as pointing upstream during Shreve ordering must be corrected by flipping their direction.
- Start an edit session, select the polyline you wish to flip the direction and click on the Edit Vertices tool. Note the vertices are shown as a sequence of green squares, terminating at a red square. The red vertex is the To-node of the polyline
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- Right click on the selected polyline and select Reverse Direction from the menu. Note that the red vertex will swap to the other end of the polyline, indicating the polyline has been flipped.
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 Flipping a polyline alters the direction of the geometry, it does not swap node values in the attribute table. To ensure the topological information is in sync with the geometry you must re-run your network through the Extract Network Topology and write to Workspace tool to rebuild and correctly attribute the node and polyline fields in your river network.
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