Think of it like a world atlas, in printed media. There's the map of the world, then continent maps, country maps, city maps. Each on a separate page. By necessity. In digital domain, if you had the necessary resolution, all you need is the world map. To see a city, you just zoom in to the desired spot. Hmmmm. Sounds Google maps! Except, they cheat, because the required resolution does not exist, plus, a single file would be very large! So, without a sophisticated zoom algorithm, the next best is to use "pages" with good indexing, labeling, and linking techniques.