Linear referencing - how does Arc decide which end of a line to start with?

KeithAddison1

Using ArcMap 10.3.1 - I applied linear referencing to a big tangled looping around on itself many times mass of separate polylines (I didn't combine any of them, all had a unique identifier) I used the two fields option as the measure source with a FROM and TO attribute field.  What I haven't been able to figure out is how the program determined which end of the polyline to use as the starting point (the FROM field) and which to use as the end point (the TO field).   How does Arc determine this? 

TedKowal

The LRS will by default increase in the "Direction" in which the line originally drawn.  (You can change this behavior).

So in order to visualize in which direction each line segment is increasing I go to the Line properties symbolization and choose a symbol with an arrow head at the "end" of the line going in the direction of travel (increasing length).

Circled in the image is where you can set more "arrowheads" distributed along each line segment for even better visualization.

Hope this helps somewhat --  the only other way I know is programmatically where you calculate the measures start and end and repopulate the From to accordingly and test each segment for increasing values highlighting the ones out order.