Well, the outer edge of the city you see when flying is at about 5000-6000 m from the center of the city (the edge of the buildings, not the landscape, thats at 10000 m). Thats about 95 000 000 square meters. The maps are usually 800*800 m and there are 9 sites (since you revisit two maps), thats 5 760 000 so about 1/16 of the city is represented in the maps. I might have calculated wrong, it's early in the morning over here but it seems about right.
But in theory everything is possible... there is a editor out there soon