Google Earth shots.

This is an overhead view of the city. You can see the river to the North and the airport to the East. Across the river is what the locals call Willow Island. The city has around two million population. It doesn't look that big on the map but most of the buildings are eight floors high and most of the downtown buildings are 20 to 30 floors high. In the zoomed in picture you can see a marker labeled 'starting location'. This is the city center square which is on top of 'Fu-Mart'. 'Fu-Mart is the single biggest underground market and is the center for the entire underground shopping. The underground stretchs in all directions for nearly three blocks. Our building, which is #4, is eight floors high; ten seperate entrances, called gates, access the building. Our gate is #5, and there our are two apartments on each floor of each gate, and ours is #2. I figure there is an average of five people on each floor of each gate. That makes 400 in each building. Our community has 12 buildings for a total of 4,800 people. There are communities like ours all around us. That makes close to 50,000 people living within one square mile.