Using Global Positioning Systems in the Outdoors, 4th Edition The fourth edition covers improvements in GPS accuracy as a result of WASS (Wide Area Augmentation System). Many new GPS receivers now accept corrective signals from this system of satellites and ground stations. WASS is referred to in every section of the book describing accuracy. The updated title has a new chapter explaining how to download maps and computer software to a GPS receiver, including examples readers can follow. Lawrence Letham, an electrical engineer, is an avid hiker and camper long fascinated by maps and the art of navigation. He lives in Arizona.