Engineers designing and installing outdoor and indoor wireless communications systems need effective and practical tools to help them determine base station antenna locations for adequate signal coverage, Computer-based radio propagation prediction tools are now often used in designing these systems, In this paper, we assess the performance of such a propagation tool based on ray-tracing and advanced computational methods. We have compared its predictions with outdoor experimental data collected in Manhattan and Boston (at 900 MHz and 2 GHz), The comparisons show that the computer-based propagation tool can predict signal strengths in these environments with very good accuracy. The prediction errors are within 6 dB in both mean and standard deviation, This shows that simulations, rather than costly field measurements, can lead to accurate determination of the coverage area for a given system design.