Well he's standing by a relatively large Lake, not sure where that is on the respective map, but if we're to assume that that white spec is Hyrule Castle, and Hyrule Castle is similar in size to that of TP, which according to Hyrule Historia is about 42 meters (or the concept of it is at least) than yeah it'd seem reasonable that what we saw in the E3 shot is a relatively good portion of the whole map from the position of the south part of the map or at least close to one of the lakes at the bottom. As for the chunk in the middle being Hyrule, I'm not sure about that, I mean on hand the shape kinda matches TP Hyrule, but it'd lack the volcano, which means no Death Mountain.