You can drop on an arrow but the difficult part would be getting the arrow head to be facing the correct direction. To do this at the very least you're going to need trig to know which direction each vector is facing. Alternatively you can number the stops or colour the line to show light to dark from 1st to last. Past that I don't have enough imagination to know how to put an arrow head shape at varying angles. Is there a reason why you need these to show directional arrows specifically or is the general goal to see on a map where things are heading? Changing line thickness based on the same item as path id often can work as well. So that the start point is skinny and the end point is larger.
Thanks Carl, appreciate the help.
The general goal is indeed to show the general direction.
The main reason I can't use what you suggested is that both colours and size marks are being used for other indicators. Labeling them is also not very ideal as each line is made out of hundreds of points in a small area.
Do you think it is possible to let each line show some sort of label indicating start and end when click?
The lines are pretty dense hence this suggestion.