A fundamental problem in robotics is that of exploring an unknown environment. Most current approaches to exploration make use of a global distance metric that is used to relate past sensory experiences to local measurements. Rather than rely on such an assumption we consider the more general problem of exploration without a distance metric, as is typical of exploring using only visual information: we propose robot exploration as graph building. In earlier papers we have shown that it is not possible for a robot to successfully explore a metricless environment without aid, but that by augmenting the robot with a single marker (which can be put down or picked up at will) it is possible for a robot to map its environment. In this paper we present the extension of our algorithm to the case of k markers, and comment on the resulting decrease in time for exploration. By defining a minimal model for the world and the sensory ability of the robot, we separate spatial reasoning from visual perception. In this paper we deal only with the spa-tial reasoning component of the exploration problem, and assume that visual perception can identify the marker and the edges incident on the current location.