| In this paper, we describe the use of a broadband, frequency-modulated sonar sensor (a CTFM sonar) for generating maps of structured environments for robots and autonomous systems. The major advantage of using these sensors is that the information generated is reliable enough to extract the geometry and type of certain features with very few measurements; hence, maps can be generated rapidly. Although the technology of low-cost CTFM sonar has been available for some time, it has only very recently been considered seriously as a candidate sensor for navigation and mapping in spite of its superior performance. We describe the operation of the sensor and the use of both the range-orientation and amplitude-orientation profiles to extract information online and point targets in both smooth and rough environments. We demonstrate the method through generating a map for a room typical of a modern building (in fact, in a domestic house), using resolution of scanning increment from 1.8 deg down to 10.8 deg. We examine the robustness of the method as the number of measurements is reduced through introducing two quality metrics for each map.