If you have an AT or PCT databook, it's a lot like those that except substitute westbound/eastbound with northbound/southbound. If you've done section or thru-hiking before and just need to know what's ahead of you, this book is great.
The databook is a good alternative or complement to the CMC press 'official guidebook', so I'm just going to make that comparison alone. Don't get me wrong, the guidebook is a great resource also full of 'Gudy's tips' and some other casual hiker fluff such as wildlife ethics, hiking lore, how-to-pack, going light, etc; but this databook doesn't have any of that stuff. Instead it is compact, lighter and gives a good at-a-glance breakdown of just mileage, milestones/towns, elevation and most importantly water sources and resupply opportunities.