they tend to think of certain things.

They think of buildings and streets

and skyscrapers, noisy cabs.

But when I think about cities,

I think about people.

Cities are fundamentally about people,

and where people go

and where people meet

are at the core of what makes a city work.

So even more important than buildings in a city

are the public spaces in between them.

And today, some of the most transformative

changes in cities

are happening in these public spaces.

So I believe that lively, enjoyable public spaces

are the key to planning a great city.

They are what makes it come alive.

But what makes a public space work?

What attracts people to successful public spaces,

and what is it about unsuccessful places

that keeps people away?

I thought, if I could answer those questions,

I could make a huge contribution to my city.

But one of the more wonky things about me

is that I am an animal behaviorist,

and I use those skills not to study animal behavior

but to study how people in cities

use city public spaces.

One of the first spaces that I studied

was this little vest pocket park called Paley Park

in midtown Manhattan.

This little space became a small phenomenon,

and because it had such a profound impact

on New Yorkers,

it made an enormous impression on me.

I studied this park very early on in my career

because it happened to have been built

by my stepfather,

so I knew that places like Paley Park

didn't happen by accident.

I saw firsthand that they required

incredible dedication

and enormous attention to detail.

But what was it about this space

that made it special and drew people to it?

Well, I would sit in the park and watch very carefully,

and first among other things

were the comfortable, movable chairs.

People would come in, find their own seat,

move it a bit, actually, and then stay a while,

and then interestingly,

people themselves attracted other people,

and ironically, I felt more peaceful

if there were other people around.

And it was green.

This little park provided what New Yorkers crave:

comfort and greenery.

But my question was,

why weren't there more places with greenery

and places to sit in the middle of the city

where you didn't feel alone,

or like a trespasser?

Unfortunately, that's not how cities

were being designed.

So here you see a familiar sight.

This is how plazas have been designed for generations.

They have that stylish, Spartan look

that we often associate with modern architecture,

but it's not surprising that people

avoid spaces like this.

They not only look desolate,

they feel downright dangerous.

I mean, where would you sit here?

What would you do here?

But architects love them.

They are plinths for their creations.

They might tolerate a sculpture or two,

but that's about it.

And for developers, they are ideal.

There's nothing to water, nothing to maintain,

and no undesirable people to worry about.

But don't you think this is a waste?

For me, becoming a city planner

meant being able to truly change the city

that I lived in and loved.

I wanted to be able to create places

that would give you the feeling that you got

in Paley Park,

and not allow developers to build bleak plazas like this.

But over the many years,

I have learned how hard it is

to create successful, meaningful,

enjoyable public spaces.

As I learned from my stepfather,

they certainly do not happen by accident,

especially in a city like New York,

where public space has to be fought for to begin with,

and then for them to be successful,

somebody has to think very hard

about every detail.

Now, open spaces in cities are opportunities.

Yes, they are opportunities for commercial investment,

but they are also opportunities for the common good

of the city,

and those two goals are often not aligned with one another,

and therein lies the conflict.

The first opportunity I had to fight

for a great public open space was in the early 1980s,

when I was leading a team of planners

at a gigantic landfill called Battery Park City

in lower Manhattan on the Hudson River.

And this sandy wasteland had lain barren

for 10 years,

and we were told, unless we found a developer

in six months, it would go bankrupt.

So we came up with a radical,

almost insane idea.

Instead of building a park

as a complement to future development,

why don't we reverse that equation

and build a small but very high-quality

public open space first,

and see if that made a difference.

So we only could afford to build a two-block section

of what would become a mile-long esplanade,

so whatever we built had to be perfect.

So just to make sure, I insisted

that we build a mock-up

in wood, at scale, of the railing and the sea wall.

And when I sat down on that test bench

with sand still swirling all around me,

the railing hit exactly at eye level,

blocking my view and ruining my experience

at the water's edge.

So you see, details really do make a difference.

But design is not just how something looks,

it's how your body feels on that seat in that space,

and I believe that successful design always depends

on that very individual experience.

In this photo, everything looks very finished,

but that granite edge, those lights,

the back on that bench,

the trees in planting,

and the many different kinds of places to sit

were all little battles that turned this project

into a place that people wanted to be.

Now, this proved very valuable 20 years later

when Michael Bloomberg asked me to be

his planning commissioner

and put me in charge of shaping

the entire city of New York.

And he said to me on that very day,

he said that New York was projected

to grow from eight to nine million people.

And he asked me,

"So where are you going to put

one million additional New Yorkers?"

Well, I didn't have any idea.

Now, you know that New York does

place a high value on attracting immigrants,

so we were excited about the prospect of growth,

but honestly, where were we going to grow

in a city that was already built out to its edges

and surrounded by water?

How were we going to find housing

for that many new New Yorkers?

And if we couldn't spread out,

which was probably a good thing,

where could new housing go?

And what about cars?

Our city couldn't possibly handle any more cars.

So what were we going to do?

If we couldn't spread out, we had to go up.

And if we had to go up,

we had to go up in places

where you wouldn't need to own a car.

So that meant using one of our greatest assets:

our transit system.

But we had never before thought

of how we could make the most of it.

So here was the answer to our puzzle.

If we were to channel and redirect

all new development around transit,

we could actually handle that population increase,

we thought.

And so here was the plan,

what we really needed to do:

We needed to redo our zoning --

and zoning is the city planner's regulatory tool --

and basically reshape the entire city,

targeting where new development could go

and prohibiting any development at all

in our car-oriented,

suburban-style neighborhoods.

Well, this was an unbelievably ambitious idea,

ambitious because communities

had to approve those plans.

So how was I going to get this done?

By listening. So I began listening,

in fact, thousands of hours of listening

just to establish trust.

You know, communities can tell

whether or not you understand their neighborhoods.

It's not something you can just fake.

And so I began walking.

I can't tell you how many blocks I walked,

in sweltering summers, in freezing winters,

year after year,

just so I could get to understand

the DNA of each neighborhood

and know what each street felt like.

I became an incredibly geeky zoning expert,

finding ways that zoning could address

communities' concerns.

So little by little, neighborhood by neighborhood,

block by block,

we began to set height limits

so that all new development

would be predictable and near transit.

Over the course of 12 years,

we were able to rezone

124 neighborhoods,

40 percent of the city,

12,500 blocks, so that now,

90 percent of all new development of New York

is within a 10-minute walk of a subway.

In other words, nobody in those new buildings

needs to own a car.

Well, those rezonings were exhausting

and enervating and important,

but rezoning was never my mission.

You can't see zoning and you can't feel zoning.

My mission was always to create

great public spaces.

So in the areas where we zoned for significant development,

I was determined to create places

that would make a difference in people's lives.

Here you see what was

two miles of abandoned, degraded waterfront

in the neighborhoods of Greenpoint

and Williamsburg in Brooklyn,

impossible to get to and impossible to use.

Now the zoning here was massive,

so I felt an obligation to create

magnificent parks on these waterfronts,

and I spent an incredible amount of time

on every square inch of these plans.

I wanted to make sure that there were

tree-lined paths from the upland to the water,

that there were trees and plantings everywhere,

and, of course, lots and lots of places to sit.

Honestly, I had no idea how it would turn out.

I had to have faith.

But I put everything that I had studied and learned

into those plans.

And then it opened,

and I have to tell you, it was incredible.