Manhattan density, and benefits

http://www.nytimes.com/2012/03/04/realestate/how-many-people-can-manhattan-hold.html?_r=1&pagewanted=all
Manhattan has 1.6 million, had 2.3 million people in 1910.
Workday population doubles to 3.9 million. Thanksgiving Day Parade can see 5 million.
Top Hong Kong density would mean 2.6 million.
Kowloon Walled City density could mean 65 million.

http://www.theatlanticcities.com/neighborhoods/2012/03/los-angeles-seeks-pedestrians/1410/

http://www.theatlanticcities.com/technology/2012/03/why-driverless-cars-would-be-bad-cities-and-suburbs-alike/1393/

location affordability
http://www.theatlanticcities.com/housing/2012/02/how-more-expensive-housing-can-actually-cost-you-less/1347/
http://switchboard.nrdc.org/blogs/kbenfield/cnt_takes_location_efficiency.html