1. A method for navigating a robotic garden tool operating in a lawn within a predetermined working area defined by boundaries, which robotic garden tool is provided with at least one sensor unit configured to detect the boundaries, and wherein the robotic garden tool is configured to operate in the working area in an irregular pattern, the method comprising: dividing the working area into subareas; providing the robotic garden tool with a low-accuracy positioning device for defining the subareas based on coordinates from the low-accuracy positioning device in the robotic garden tool; storing the coordinates for the subareas in the robotic garden tool, receiving coordinates for an approximate position of the robotic garden tool from the low-accuracy positioning device; and providing the robotic garden tool with a processor for comparing the stored coordinates for the subareas, with the coordinates for an approximate position of the robotic garden tool from the low-accuracy positioning device, to determine in which subarea the robotic garden tool is at present.