There are a few ways to set the direction of the flows for a line:
- using the digitized direction (i.e. lines are always digitized in the direction of the flow)
- using an attribute indicating the direction relative to the digitized direction of the flow (with, against, indeterminate).
- using a more complex scheme (related table, etc.) when the direction may change (e.g. tidal flows)
If the flows are always going one way it is a good practice to have the digitized direction matching the flows.
If you build a geometric network with the lines, you can set the flow direction in the line based on the digitized direction (with/against) or based on attribute in each line feature. Note that the flow direction is always uninitialized in a new geometric network (except the one we build in Arc Hydro) and needs to be set specifically to be able to perform upstream or downstream traces. If you edit the lines in the network, you will also have to reset their flow direction.
Christine Dartiguenave
Esri Water Resources Team
