Flip the direction of a polyline

How to flip the direction of a polyline

For the network algorithms to process correctly all polylines must point in a source to mouth direction.

Polylines labelled zero from Strahler ordering or recognised as pointing upstream during Shreve ordering must be corrected.

The rest of this page talks you through the process of how to flip an individual polyline. If you have hundreds of polylines to flip then you should seek tools available from the ESRI ArcScript website.

Flipping a polyline alters the direction of the line and does not swap node values in the attribute table. You must change these manually or re-run RivEX and compute the new node ID values.

Load your river network into ArcMap and display the Editor tool bar.

Editor button

Start an edit session.

Set task to Modify Feature and ensure the Target is your river network. Finally select the Edit Tool.

Editor toolbar

Using the Edit Tool select the polyline that requires flipping. It's vertices will display as green squares. The red vertex is the To-Node.

Polyline vertices

Right click on the selected polyline and select Flip from the menu. Note that the red vertex will swap to the other end of the polyline, indicating the polyline has been flipped.

Context menu

Stop editing to save your changes.

Stopping editing

Remember you must update the To- and From- node fields to reflect the change of direction. You can do this manually by editing the record or allowing RivEX to rebuild them for you after you have saved you edits.

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