A robotic system for systematically moving about an area to be covered. The system includes at least one boundary marker (48) located along the outer edge of the area to be covered, a robot (40) with a navigation system (41) that navigates the robot (40) in generally straight, parallel lines from an initial location and turns the robot (40) when the robot (40) encounters one of the boundary markers (48), thereby to systematically move about the area to be covered. The sensor unit (43) senses proximity to one of the at least one boundary marker (48).