The Marine Aids Program of the Canadian Coast Guard, Department of Fisheries and Oceans, is responsible for the review of aids to navigation systems to ensure the provision of equitable, safe, and cost-effective marine transportation. Aids system reviews have traditionally been carried out using paper hydrographic charts, graphs, and tables and have been very labor intensive. In an effort to improve the efficiency of the marine aids review process, the Marine Aids Program Review Analytical Tool (MAPRAT) has been developed using Esri's ArcView GIS. The result is the ability to analyze various aids system design options under various climatic conditions and using known vessel routes. This project has resulted in some significant firsts: it is the first implementation of GIS in the area of marine aids locational analysis and, to the best of our knowledge, the first use of Canadian Hydrographic Service nautical charts within an Esri application.