"Reaching back to the sixth century, the guide book tradition always focused on Rome, the center of religious power and of ancient culture. In the seventeenth and eighteenth centuries, serving an increasing number of travelers, the guidebooks matured as a literary form. [...] The structure of the guidebooks may be described as a grid. Horizontally, they established an itinerary, a sequence of cities and sights, usually along the road to and from Rome. Vertically, they recorded the role of each place in history and art. The itinerary exchanged the seamless geography of Italy for a blank map dotted with points of interest.
Peter Galassi, Corot in Italy: Open-Air Painting and the Classical-Landscape Tradition