The Economist - USA (2019-10-05)

Cityextent 1980 2014

Increasingurbandensity

Decreasingurbandensity

Kinshasa,Congois densely

populatedbecausepeople

squeezeintosmallhomes

Dhaka,Bangladeshis low-rise,

buthomescovermuchofthe

cityandaretightlypacked

Minneapolis-StPaul,UnitedStatesis a low-rise

metropoliswherepeoplehaveplentyofelbowroom

HongKongis high-rise,but

residentialbuildingscovera

tinyproportionofitstotalarea

Populationv urbandensity,1990-2014 Howdifferentcitiesgrow

Mostcitiesarebecominglessdenseastheirpopulationsincrease.Thebiggestengineofgrowthissprawl,notbuildingheight

Bogotá

Dhaka

Hangzhou

Karachi

London

Manila

Shenzhen

1990 2000 2014

10,000 100,000 1m 10m

0

100

200

300

400

0

100

200

300

400

Peopleperhectare

Accra

Bishan

Kozhikode

Kinshasa

Hindupur Hong

Kong

Jaipur Kolkata

Mumbai

Seoul

To k y o

NewYork

10,000 100,000 1m 10m

Population,logscale

Population,logscale

Peopleper

hectare

Minneapolis

Crowding

Populationper

floorarea

Buildingheight

Ratiooffloorareatofootprint

ofresidentialbuildings

Threecomponents

ofurbandensity

Coverage

Proportionofcity

occupiedbyhomes

Nine-city

average*

Belowaverageon

allthreemeasures

Building

height

Coverage

Crowding

Sources:AtlasofUrbanExpansion;“AnatomyofdensityI: sixmeasurablefactorsthattogether

constituteurbandensity(forthcoming)”byShlomoAngelandPatrickLamson-Hall(2019)

*Bangkok,Bogotá,Cairo,Dhaka,HongKong,Kinshasa,Madrid,Minneapolis-StPaul,Wuhan

5 km 5 km

10 km

5 km

TheEconomistOctober 5th 2019 81

L

ook up, andcities seem to be squeezing

in more people. All of the world’s 73 resi-

dential towers over 250 metres high were

built after the year 2000. Another 64 are

under construction. On 57th Street in New

York, a building where The Economistused

to have an office has been knocked down

and replaced by an 82-storey glass splinter.

When finished, it will be just 8 metres shor-

ter than the Empire State Building.

But appearances can deceive. Shlomo

Angel and researchers at the Urban Expan-

sion Programme at New York University

have used population data and satellite

maps to show that most cities are becom-

ing less densely populated. That is seldom

because they are losing people (although

New York is). Usually, it is because they

grow faster in extent than in population. In

1990-2014, for example, Mexico City grew

from 9.8m inhabitants to 17.8m, an 82%

gain. During the same period, however, its

built-up area expanded by 128%. This pat-

tern is common. Sprawl has outpaced den-

sification in 155 of the 200 cities tracked by

the Urban Expansion Programme.

As people grow richer, they demand

more space. Despite the efforts of many ur-

ban planners to stop them, they move from

cramped inner cities to sparsely populated

fringes (Mr Angel’s team counts suburbs as

parts of cities, regardless of where political

boundaries lie). Moreover, because people

are living longer and having fewer chil-

dren, a growing proportion of households

contain only one or two people.

Even the towers that spring up in city

centres are not all that dense. There is a lot

of air between them and a lot of elevator

shafts inside them. High-rise cities like

Seoul and Tokyo are less densely populated

than Dhaka, the capital of Bangladesh,

where most people live in walk-up apart-

ment buildings or low-rise slums.

Cities can be dense in different ways.

Hong Kong is a champion at stacking peo-

ple on top of each other. But almost all of

Hong Kong’s built-up area is occupied by

roads, pavements, offices, hotels, parks

and mandatory spaces between buildings.

The footprints of residential buildings ac-

count for less than 4% of it. In Dhaka, by

contrast, homes cover nearly 20% of the

land. In a poor city like Kinshasa, the capi-

tal of the Democratic Republic of Congo,

population density comes mostly from

squeezing more people into each room.

Many low-density cities wish to change.

Minneapolis, for example, plans to alter

housing codes to pack more people in. But

density always comes with drawbacks.

Towers cast shadows. Devoting more of the

city to residential buildings means less

space for other useful things—skimp on

roads and you might end up with Dhaka’s

traffic jams. And nobody should envy the

residents of Kinshasa. It is always worth

asking the advocates of higher density:

what kind, exactly, would you like? 7

Modern cities add people by spreading

out more than by building up

The paradox of

density

Graphic detailUrban growth