Maybe draw a mask path on a still image of the map using the pen tool and use the stoke effect to show it so it moves along the mask path?
You could also move the image (or pre-composition of a section of the image) as well as doing the above or (move the virtual 3D camera if the layers are set as 3D?).
Bottom layer - map
Next layer - Shape layer, draw path with pen tool (g) to create a path with not fill and stroke only traing the route then add Trim Paths and keyframe start and end of trim paths to make the line move across the map.
This is an extremely basic AE task but if you don't know anything about After Effects or creating composites you'll need to start with some basic training and get yourself up to speed on the UI and the principals of animation. You also need to know about video formats, compression, delivery formats and a few other things. I suggest that you start here: Basic AE