When a book starts with a map, you know that the setting is going to be a big deal. A lot of fantasy novels (like The Lord of the Rings and the Game of Thrones series) start off this way. The idea is to give us a handy reference guide to this entirely new world that we'll be exploring. These new lands, with their own histories, politics, and geography, really go a long way in putting the "fantasy" into fantasy novels. And Eragon is no exception.
The setting for Eragon starts in the fictional country of Alagaësia. This land is under the rule of the evil King Galbatorix, who is charge of a larger piece of land called simply "the Empire" (not that Empire). In his travels, Eragon sees a lot of Alagaësia, as he leaves his sheltered valley of Palancar and the Spine Mountains to voyage to the plains and coast and cities of his home country.
Think about that for a second. Eragon, much like us, starts off not knowing very much about this land. Luckily for us, though, he's got a burning curiosity to see what's going on beyond the borders of his sleepy little village of Carvahall. As he travels from his protective valley to the wide open plains, then to the coastal lands, as well as to the bustling cities of this world, the world of Eragon opens up before us.
That world is modeled after what we know of the so-called Middle Ages of our own time. People ride on horses instead of in cars; they use swords instead of guns; they wear robes and tunics instead of hypercolor shirts. (Maybe we've revealed too much about our fashion sense here.) It's a world that we know only through history books, but it's one that is very vividly brought to life through Eragon's explorations. We can practically hear the blacksmith hammers ringing on the anvils and the horses gallop over cobblestone streets.
As if that weren't enough, Eragon's travels lead him out of this more familiar world of Middle Age cities and villages. We go with him beyond the borders of the Empire and beyond the king's control. He crosses the mighty Hadarac Desert and makes his way through the formidable Boer Mountains. It's as if the more extreme the landscape, the more intense the challenges will be for our hero. When he comes at last to Tronjheim—a city built inside a volcano—we know that our hero will be facing his toughest challenge yet.
In all, the setting allows us the chance to explore a whole new, though not entirely alien, world. It also reflects both the comforts and challenges of our hero. Ultimately, the detailed history and geography of the book are a big part of what helped to put Eragon on the… map. (We know, we know, but we just couldn't resist.)
P.S. For more on setting, check out what we have to say about the theme of "Exploration."