The efficiency of frequency utilization in mobile radio strongly depends on the performance of handoffs. Criteria for handoffs are usually derived from measured carrier-to-interference ratios (C/I). However, in mobile radio signal levels vary so rapidly that channel allocation cannot be performed in real time for optimum C/I. On the other hand, too many handoffs reduce frequency efficiency. The determination of cell boundaries, which are not only governed by C/I, but allocated to geographical lines in the terrain avoid unnecessary handoffs. In addition to C/I auxilary data are measured in the German system C and processed to detect the cell boundaries. The improvements gained from this procedure are demonstrated by measured results.