I recently had to do this for a travel movie and found no way of doing it the way I wanted, a meandering broken line. Where it goes and whether it turns back is of no consequence.
In the end I wound up making a moving .gif file by taking the map and using layers with the line drawn in full and then erasing one element for each frame. Once all the layers are done and saved as individual gif files in sequence, you create a moving .gif file.
I use a very simple and free program called "unFreeze". Google it, it's free to download from several places.
It is an incredibly time consuming way to do it but it works because PD thankfully recognizes a moving gif file as a "video" and not a static gif