OpenStreetMap: Using and Enhancing the Free Map of the World
This book is a comprehensive guide to all aspects of OpenStreetMap, the free map of the world.
OpenStreetMap (OSM) is a map of the whole world which can be used and edited freely by everyone. In a Wikipedia-like open community process, thousands of contributors world-wide survey the planet and upload their results to the OpenStreetMap database.
If you want to become an OSM "Mapper" then this book is the ideal starting point.