Sunday, February 20, 2011

Are Skyscrapers Necessary for Density?

I just read Ed Glaeser's Atlantic piece on skyscrapers (which is excerpted from his new book on cities that I need to read).  I agree with nearly everything he says, particularly about the need for tall buildings in Mumbai, but I also think it is worth mentioning that one can get a lot of density without a lot of skyscrapers.  The municipality of Paris has a residential density of about 54,000 people per square mile; Manhattan has a residential densisity of about 71,000 people per square mile.  Paris has about 1.7 million workers, while Manhattan has about 2.1 million workers.  Yet as Ed notes, Manhattan has lots of skyscrapers, and Paris has few, and almost none outside of Le Defense.  How is this possible?

Let's look at a Google Earth image of Paris from 50,000 feet up:

Now lets's look at Manhattan from the same height:

Notice how at this scale you can see the minor streets of Manhattan pretty clearly, but not the minor streets of Paris?  Paris actually uses its land very efficiently--it does not waste space on streets or setbacks.  As a consequence, while it can be livable (if not affordable) with 3/4 of the denisity of Manhattan and a small fraction of the number of tall buildings of Manhattan.

There is no question that Ed is correct that mega-cities such as Mumbai, Cairo, Mexico City and Sao [Paulo] require skyscrapers to house people adequately and affordably.  But as he also notes, building skyscrapers is a lot more expensive than low-rise buildings.  For many cities, more efficient land-use could go a long way toward making cities more livable, more walkable, and less expensive.