Instead of using an annotation, add a subview to the view that holds your map, and set the center
s of the 2 views equal to each other. As the user pans the map, it'll look like the annotation is moving.
Then whenever you need to find the coordinate that the center "annotation" is pointing to, you can use the centerCoordinate
property of the map view.
I've done this in map box and google maps, but not in MapKit, but I think it should work just the same.