Most of Manhattan isn't actually all that tall. Just go over to Google Maps and look at it in the tilted 3D view: https://www.google.com/maps/place/New+York,+NY/@40.6654432,-...

The south end and midtown are tall, the rest is not. You can stuff way more density into Manhattan than currently exists.

And Brooklyn is shorter yet, of course. Could put way more tall buildings into Brooklyn if you wanted to.

> How do you make it significantly more dense than it already is?

Better transportation in outer burroughs will expand the supply of housing within a reasonable commute distance.

Ideas:

* Invest more in expanding public transportation. More express buses, local buses that run more frequently and on time.

* Deregulate private transportation (taxis, private buses).

* Incentivize commutes during off-peak hours.

* Encourage working remotely or flexible work schedules.

* Find ways to get tractor-trailers out of dense areas.

* Actually start enforcing double-parking and jaywalking laws (this one even pays for itself).

* Encourage business development away from already-congested areas

> The best answer for NYC is probably to aggressively gentrify as many neighborhoods as possible, which means (bluntly) displacing most lower income residents and moving in bicycle riding organic jam loving armies of hipsters.

Where exactly will you find these armies of upper-middle class people? Wages and social mobility continue to decline.

http://www.epi.org/publication/even-the-most-educated-worker...

http://www.theatlantic.com/business/archive/2015/07/america-...

That's one advantage that urban planners have. These people don't need to be upper-middle class by income. They just need to be trendy culture-wise and support the development of safe, fun neighborhoods. I have a friend in Brooklyn who pays $500/month to share a large 1 bedroom apartment with 2 other guys (all in the same room). He works at a bicycle repair shop and participates in a ton of neighborhood activities. He isn't upper middle class, but he is promoting gentrification of the neighborhood. (Unfortunately for him, that gentrification will eventually force him out unless he improves his income or purchases property.)

So, what is the most economical skycrapper that they can build in NYC? 20 stories tall? Ten stories tall?

How many buildings are at the economical height or taller? How many are lower?

Have you seen NYC? 20 stories is a small walk-up these days.

I've lived in and around NYC my entire life, and I always thought that the shape of the skyline was governed mostly by the underlying granite: lots of support for huge buildings downtown and midtown, not so much everywhere else. But in the past five years or so very tall buildings have been popping up all over. I think it won't be long until you'll have trouble finding the Empire State Building lost amongst it's bigger neighbors.

Rebuilds, upzoning, microapartments, public housing. The list is long:

https://medium.com/@opirmusic/fixing-the-nyc-rent-crisis-or-...

Read Matt Yglesias' "Rent is Too Damn High" book if you want a more thorough treatment the topic.