Most large cities, except for Hong Kong, still have plenty of room to build up. You don't tear down the 20-floor buildings to build the 40-floor ones, you tear

Most large cities, except for Hong Kong, still have plenty of room to build up. You don't tear down the 20-floor buildings to build the 40-floor ones, you tear down the 6-floor ones in the next neighborhood. It's much cheaper to buy them out.