This thesis presents an application of a geographical information system (GIS) in propagation prediction. The motivating force behind this work is the need for accurate and efficient site-specific propagation prediction tools for personal communication system (PCS) design. Site-specific information including terrain and building attributes is vast and complex, and needs specialized handling. A geographical information system provides these capabilities, and relieves the propagation analysis tools of the burden of data management. This work focused on harnessing the relevant abilities of a GIS for aiding the current propagation prediction software. GRASS (Geographical Resources Analysis Support System) GIS has been used for data handling, transformation, and analysis. Schemes and techniques were developed for operations on site-specific data as used in propagation prediction. Attention was paid to the types of data needed, available data sources and their formats, and the needs of the propagation analysis software. These schemes were implemented in the form of several new programs that have been integrated with GRASS. Data interfacing is the major function performed by these programs. Building and terrain data may now be exchanged between GRASS and AutoCAD, a computer-aided design software package. The data analysis powers of the GIS were used for estimating diffraction path loss over terrain. The results of propagation prediction can be displayed in a graphical manner through the GIS, and hardcopy outputs are possible. The work presented here sets the framework for the integration of various software modules that can combine to form a propagation prediction tool. / Master of Science