A control system is provided for navigating an autonomous machine around a working area in a manner that causes the machine to traverse substantially all of the free surface of the working area. The control system is arranged to cause the machine to follow a boundary of the working area and to perform a plurality of movements, each movement comprising the machine travelling away from the boundary of the working area, at an angle to the boundary, and returning again to the boundary. The machine moves along the boundary of the working area between each movement and repeats the movements as the machine follows substantially the entire boundary of the working area.