This book helps the mariner to correctly use his GPS for navigating lakes, rivers, and even coastal waters. The first 4 chapters are designed to teach the reader the basics of GPS operation. The rest of the book goes into more detail for using the GPS for navigation on the water. What I liked about this book is that this can also apply to those who are totally unfamiliar with using a GPS. Therefore this book can be used for the person who uses a handheld GPS for multiple purposes, hiking, hunting, fishing lakes and streams, and even driving in unfamiliar areas.