I have a stream polyline feature class that I would like to turn into a route for linear referencing. I added a field called Miles for which to base the M value is to be based. Using the Create Routes tool (in ArcGIS 10.5.1 or ArcGIS Pro 2.1.2) I'm running into a snag.
When I set the Coordinate Priority option to Upper_Right, my river miles are not correct for half the streams. Please refer to the image below. The main stream is highlighted in blue, and I have symbolized each of the tributaries with the arrow heads at the end of the line. The main stream and the tributaries that flow in from the south have their river miles correct: they increase from the source downhill to the confluence. However, the tributaries that flow in from the north are all bass-ackwards. Flipping a route segment in an edit session does not seem to correct the problem.
Bottom line: how do you create a Route of existing features and have the measurement value follow the direction of the polyline from-to?