If a man is looking up at the tip of an electric pole, then the line joining the man's eye and the tip of the electric pole is called as the line of elevation.
The line of sight is a straight line along which an observer observes an object.
It is an imaginary line that stretches between observer's eye and the object that he is looking at.
If the object being observed is above the horizontal, then the angle between the line of sight and the horizontal is called angle of elevation.