So we gave a camera looking down and out over a simple road map.
In the centre foreground is an arrow, pointing continually forward.
The map continually moves towards us, and he map rotates if the road bends.
I want the arrow to be a fixed point around where the the map rotates as the 'car' goes around a corner.
Sounds easy, but I cannot work this out. I want to be able to animate, say, the Y axis on the map to have it moving down the screen at a constant rate.
And I want the map to rotate around the fixed arrow point as corners and bends come along.
I've tried various pareting methods and a little maths, but I can't figure out how to stop the map's anchor point being fixed to rotation.
BTW - I tried a path with a camera going along it and oriented along path, but the camera kept flipping out. I may try it again if there is no solution to this.
I think the problem here is you're moving the map and not the car. This needs to mimic real life.
The way I would do this is to set up the map, arrow and a single camera pointing down looking at the arrow correctly centered on the map.
Then, make the Camera parented to the Arrow. Arrow is parent, camera is child. Now lock the camera and map, and animate the arrow along the road, turning as it goes. If this gets wonky at corners and bends (I can't see why it would), you could do a pickwhip for X/Y position (only) properties from arrow to camera and X rotation properties and avoid the child relationship.
It seems this would be most easily animated by keyframe and not expression. If you had the map moving at a constant rate, it would feel wrong at turns and corners, where in theory the car would slow down or perhaps stop before making its turns, to say nothing of acceleration/deceleration/cruise speed.
similar to raza's setup, here's a way to let ae do the rotation for you.
create a comp, add your map and make it 3d.
use the pen tool to draw the path to travel along on the map (or on any layer). then select the mask path property (so all the points are selected) and choose edit>copy.
create a new null, make it 3d, select the position property and choose edit>paste, then choose layer>transform>auto-orient and select 'along path'.
now the null should travel along you path, turning as it goes.
add a camera to the comp and parent it to the null, and set the z rotation to 90. then adjsut the null's anchor point to position the map so the path is in the center of the screen (it would be easiest to be at the stat or end point of the path in the timeline).