Sometimes termed "the bible of A.T. hiking" because of its use in essential hike planning, each year's Data Book consolidates the basic information from the 11 official ATC guidebooks into a lightweight table of distances between major A.T. shelters, road-crossings, and features. Divided to align with the guidebook volumes, the Data Book is updated each December to address trail relocations, new or removed shelters, and other changes. In addition to including codes for lodging, food, water, and other essentials, the Data Book is keyed to both the individual guidebook sections and the separate maps.