While there isn’t a direct way to symbolize a line feature in ArcGIS Pro to have a gradient that travels along its length (rather than across its width), there are a handful of workarounds to get you there. If your line is wiggly, you might have to try a more robust method, like split the line up in to equal-length segments and dynamically tie the color to an Arcade script that steps through a sequence of colors to replicate a gradient along the path. BUT, if your lines are straight, things get a lot simpler; you just have to think deviously about symbol effects and how to bend them to your cartographic will.
Here is a quick hack to apply a gradient along a straight line, how to make them all point the way you like, and how to symbolize for an incoming or outgoing sense of movement…
0:00 like, the world’s fasted intro
0:12 the gradient stroke is cool, just not for this
0:30 tricking the line into becoming a skinny polygon, with the “buffer” global symbol effect
0:50 time for a gradient along the line!
1:05 using transparency to give a sense of direction (“pew-pew-pew” cartography)
1:26 forcing a cohesive direction
2:19 nitty gritty stuff like thickness and alternative effects
3:08 the office
Curious about how to make an origin-destination map, like my example here of the University of Michigan football team’s hometowns? Here’s a one-minute how-to. How about that basemap? Here’s how to construct it.
Love, John