The hidden role of people in understanding how cities work
[Applause]
why do we live in cities
and why do most cities worldwide
continue to grow
we might not have a clear answer to
these pressing questions as yet
but what is pretty clear is that cities
are the engines of
economic growth innovation and wealth
creation
and that to achieve this cities actually
need to connect us
their people cities bring together
people with different skills and
backgrounds
interests and cultures which then sparks
new ideas and
trends and creates new jobs
in fact empirical evidence shows that
not only wealth indicators like per
capita gdp
tend to increase with city population
size
we have found that human interactions
accelerate at
almost exactly the same pace in other
words
the interactions between the people are
key for the social
and economic functioning of cities
this fundamental role of human
interactions
is thus absolutely crucial for urban
planners
who are responsible for the design of
public spaces and infrastructures
that should facilitate the connectivity
between the people
in the past urban planning has indeed
often been quite successful
leading to attractive public spaces that
are now frequented by many people from
all walks of life
but unfortunately there are also
numerous cases where urban planning
interventions didn’t lead to the desired
outcomes
as is manifested in empty and sterile
plazas
traffic jams or even social segregation
what makes it then so hard to design
well-functioning cities well one of the
reason
is that in the past we didn’t
sufficiently understand
how people actually make use of urban
space
let’s just have a look at manhattan in
new york
we see people coming and going we see
taxi drivers going there for work
we see new yorkers who might go there
for shopping
or we see tourists who might go there
just once in a lifetime from very far
away
there is a myriad of different interests
and preferences that bring people here
and the result looks pretty random and
chaotic right
unfortunately it is exactly such
seemingly chaotic patterns
that urban planners need to deal with
when trying to avoid potential planning
pitfalls
but what if i told you that these
movements we just saw
are not at all random or chaotic but
that they are surprisingly structured
and predictable and that they follow
hidden regularities
that provide powerful guidelines for
urban planning
imagine you’re standing on a public
plaza which is full of people
coming and going now imagine you ask
all these people from how far away they
are actually coming from
this is exactly what my collaborators
and i did for boston in the u.s except
that we didn’t need to stand on a plaza
for several days
instead we could analyze millions of
anonymized mobile phone location data
that have been provided to us for
scientific purposes
and in an aggregate form so as to ensure
data privacy
so here is the result of our simple poll
for newbury street
a famous shopping area in boston on the
horizontal axis
we have from how far people visited
newbury street
and on the vertical axis we have the
number of visitors
just to be precise each data point is
the number of visitors
coming from a one square kilometer area
at the given distance away
and what we see is that if we go further
away from newbury street
we have less people coming this is of
course
nothing really surprising right who
wants to travel
all through the city just to do the
groceries
however our data now allow us to go one
step
further and to also ask how often people
are actually coming
here our same result except that we now
distinguish
between how often each person visits
newbury street
red is the number of people coming about
once per month
green is the number of people coming
about four times a month
and yellow is the number of people
coming about 10 times a month
and what we see is that the number of
visitors
also decreases the more often they are
coming
so we already start to see some very
systematic patterns
in this seemingly chaotic movement of
people right
but now comes the really surprising part
all these patterns
can actually be predicted by a simple
but
powerful mathematical travel law all
that really matters
is to just multiply the distance with
the number of visits
for instance the number of people coming
once per month
from 20 kilometers which is the red
square here
is about the same as the number of
people coming about four times from five
kilometers
which is the green square here and it is
also about the same as the number of
people
visiting ten times from two kilometers
since if we multiply a distance with the
number of visits
we always get 20.
so in our simple poll we can simply
multiply
distance with the number of visits and
all our data points beautifully line up
let me put it this way if i spend just
one day
measuring how many people come to
newbury street
i immediately know how many people will
come over the next weeks from
1 2 or 10 kilometers away and how many
of them will visit once
twice or 10 times a month and you know
what the best part is
this travel law isn’t well it only for
newberry street
it applies to virtually all locations in
the greater boston area
actually let me rephrase even this it
happens
all across the world we looked into more
data
and found that the very same travel law
holds for cities in europe
africa and asia regardless of the
detailed geographies
cultures or levels of development this
travel law is pretty amazing isn’t it
but how can it now help urban planners
to design great public spaces
well first of all having an idea of how
far
and how often people are willing to
travel helps to spot the best locations
to put the new public space such as a
park
and to have an estimate of how many
people such a new park can potentially
attract
second infrastructure planning
predictions of the population flows
especially to new urban developments is
essential
for the planning of public transport and
also for other infrastructures
we are actually applying exactly this
idea now
to support the electrification process
in a developing country
and third if we look at existing places
and if we compare the actual number of
visitors to our predictions
we can immediately identify those
locations
that attract less people than we would
actually expect
this signals a clear need to make such a
space more accessible or inviting
for additional population groups this
travel law is just one example of how
more science-based approach to cities
can help urban planning we are actually
just at the very beginning of revealing
many more of such exciting
and powerful regularities of how humans
connect to each other in urban space
cities are very complex there will
always be uncertainties
in doing such predictions for urban
planning think of bushwick brooklyn in
new york
neighborhoods that suddenly become hip
and trendy leading to escalating housing
prices
it is just very hard to predict such
dynamics
therefore it is not sufficient to
understand the basic laws of cities such
as the one i just showed
we additionally need to have early
warning indicators
that alert us of negative developments
such as social segregation
science-based approaches can certainly
help us here as well
and i’m pretty confident that we will
soon be able
to gain a much better understanding of
how to build
and maintain cities that truly enable
many diverse human interactions thank
you