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URBAN DYNAMIC LAWS AND OUR
DEGREES OF FREEDOM FOR DEVELOPMENT
Francisco J. Martínez Universidad de Chile
Instituto Sistemas Complejos de Ingeniería
tc
N(t)
t
C( ) !N t = ¥
tc
N(t)
t
tc
N(t)
t
INTERNATIONAL WORKSHOP ON URBAN TRANSPORT SUSTAINABILITY, Sept. 2-4 2013
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FROM URBAN DYNAMICS TO SUTAINABLE CITIES
1. STATITICAL EVIDENCE
2. THEORETICAL SUPPORT
3. RELEVANT IMPLICATIONS
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FROM URBAN DYNAMICS TO SUTAINABLE CITIES
1. STATITICAL EVIDENCE 2. THEORETICAL SUPPORT
3. RELEVANT IMPLICATIONS
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4
Power law in organims’ dynamics
TED Talks (www.ted.com) Geoffrey West: The surprising math of cities and corporations
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Blue Whale
2*108 g
Shrew
2g
Elephant
2*106
Mamals’ mass vary 8 orders of magnitud (108)
Shrew 2g Elephant 2*106
Blue Whale 2*108 g Blue Whale 2*108 (National Geographic)
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Metabolism rate: B=M3/4
Hemmingson 1960
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• Cities’ Goerge K. Zipf’s laws (Gabaix, 1999)
• Power laws (Bettencourt, West, et al 2007,2008)
Evidence of “natural” laws in cities?
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America’s Cities Zipf’s laws
Argentina y = -1,1492x + 15,532
R² = 0,98308
0,0
2,0
4,0
6,0
8,0
10,0
12,0
14,0
16,0
18,0
0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0
Canada Colombia
Mexico United States Venezuela
Zipf in graphs America
log(rank ) = b log( population)
Log rank
Log
po
pu
lati
on
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Europe Cities Zipf’s laws
Zipf in graphs Europe
Austria Belgium Bulgaria
France Italy Netherlands
log(rank ) = b log( population)
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10
Power laws for cities size Y/Y0=Nβ
Y: City variable (input and outputs)
N : Population
Y0 : Base line, specific for each
economy or country
β: Scale factor, common across cities
and countries
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DEVELOPED WORLD CITIES’ POWER LAWS
log(Y /Y0) = b log(N )
BETTENCOURT, LOBO, WEST (EUR. PHYS. J, 2008)
Ou
tpu
ts
Inp
uts
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Table1:ScaleparametersforChileancitiesandregions
ObservationUnit
Nrofobservations
IndependentVariable
Parameterestimates
β ln(y0)
County* 19Roadsnetwork
(km)0.85
(9,72)-3.80
(-3,57)
Region** 13Totalenergyconsumption
(GWH)
0.87(4,19)
-4.09(-1,44)
City 148 Area(ha)0.91
(74,41)-3.20
(-26,35)
County 19 Urbanbusfleet0.93
(5,03)-5.38
(-2,37)
County 19 Carfleet 1.00(15,96)
-1.97(-2,58)
Region 15Residentialenergy
consumption(GWh)
1.08(7,17)
-8.96(-4,43)
Region 15Residentialenergy
consumption(GWh)
1.08(7,17)
-8.96(-4,43)
Region 15 Terciaryeducationvacancies
1.16(8,80)
-5.61(-3,17)
County 24Rich
Population1.25
(12,48)-5.79
(-4,72)
County 12 ResearchProjects1.51
(5,35)-17.42(-4,71)
log(Y /Y0) = b log(N )
Ou
tpu
ts
Inp
uts
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Kuhnert, Helbing & West, Physica A363, 96-103 (2003)
Scale Economies Sub linear: gas stations, roads, non-residential, energy…
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Increasing returns Super linear: income, PGB, patents, crime
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Three cases from empirical evidence statistically constant parameters
i) b ~ 0.8 < 1 INFRAESTRUCTURE (BIOLOGY) SUB-LINEAR ECONOMIES OF SCALE FROM EFICIENTCY
ii) b = 1
LINEAR NOT-INNOVATIVE
iii) b ~ 1.15 >1 SOCIO-ECONOMIC ¿SURPRISING?
SUPER-LINEAR INNOVATION
* Combined forces to concentration in large cities * Power laws accelerate system’s dynamics
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CONCLUSIONS from evidence
• Power factors are statistically constant for the set of analyzed cities
• Returns to scale: super-linear creation of wealth and innovation beta>1 .
• Economies of scale: sub-linear infrastructure costs beta<1.
* Combined forces to concentration in large cities
* Power laws accelerate system’s dynamics
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FROM URBAN DYNAMICS TO SUTAINABLE CITIES
1. STATITICAL EVIDENCE
2. THEORETICAL SUPPORT 3. RELEVANT IMPLICATIONS
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18
TOWARDS A FUNDAMENTAL THEORY OF THE
EVOLUTION OF CITIES
Maurice René Fréchet (1878 - 1973)
Thesis: The power law emerges from agents’ behavior: • Maximization (rational?) choice among options • Random events
Alternative physics based model in two papers: Bettencourt and Batty, both in Science, June 2013
Emil Julius Gumbel (1891 – 1996)
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• Agents: individuals/households and firms
• Behavioral perspective:
– Individuals max satisfaction, Firms max profit
– Discrete random choice of activities (McFadden-Gumbel Type I)
– Market prices on goods and services
– Agents’ interaction on economic and social structures
• Land Auction – Competitive auctions (Alonso)
– Agents random bids (Fréchet – Type II)
Power Laws
Welfare power law W ³ A ×N g
R = A ×N g Rents power law
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Households’ Optimal Choices conditional on location
wni
=1
mni
ln exp(mniwnik
)k
åæ
èçö
ø÷
wnikj
( pkj
+ tij)
wnik
wni
wnik
=1
mnik
ln exp(mnik
wnikj
)j
åæ
èç
ö
ø÷
whi
=1
mhi
ln exp(mhiwni
)n
åæ
èçö
ø÷whi
(Ph 'i
,ri)Household
Individual
Activities
Trip Destinations
Pnikj
Pnik
Pni
Prices, Transport
General social and economic equilibrium conditions apply, conditional on location.
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Firms’ Optimal Choices conditional on location
pki
=1
mki
ln exp(mkipnik
)n
åæ
èçö
ø÷
pnik -k ' j '
( pkj
+ tkij
)
pnik
pki
(Pk '
,ri)
pnik
=1
mnik
ln exp(mnik
pnik -k ' j '
)k ' j '
åæ
èç
ö
ø÷
pk
=1
mk
ln exp(mk(p
ki- r
i))
i
åæ
èçö
ø÷pk
Location
Industry
Firms
Input-output Spatial interaction
Pnikj
D ,S
Pnik
Pni
Agglomeration, Rents
Prices, Transport
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Alonso’s Land Allocation: landowners max profit, best bidder rule
r1
w11 w21
r2
w12 w22
h1 h2
Bids
Rents
Agents
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Mattson, Weibull, Lindberg (2011)
The Fréchet Model
• Fréchet, extreme value (Type II) of positive variables.
• Agent’s bids: independent θni~Fréchet(β,vni), vni>0, and β>1.
• Auctions: rents are max bids, Fréchet(β,ri)
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Remarks: rents power Law
• Rents scale super-linear with population (even for V constant)
• Scale factor defined by beta: agents’ diversity
• Betas from agents’ Gumbel utility: emerges from micro behavior
• Economies of scale (alfa=0)
• Numeraire price factor R0
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THEOREM
At the city’s long term market equilibrium, total (consumers plus suppliers) welfare is given by the following power law:
and for economies with non-negative economies of scale it represents a super-linear power law.
with γ = 1 + 1/beta + alpha >1
Population Variance
Economies of scales
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URBAN GROWTH
Resources =
• Maintenance: cost of current population
• Investment: grow up babies (education, food,…)
Bettencourt, et al. (2007, 2008)
Maintenance
Growth
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Urban Growth Dynamics
C( ) !N t = ¥
T
N(t)
tc
N(t)
t
N(0)
t
• Cities super-linear dynamics
• Time horizon T defines singularity
• T decreases with living cost R0 and N0
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Urban Growth Dynamics
tc
N(t)
t
C( ) !N t = ¥
T
N(t)
tc
N(t)
t
tc
N(t)
t
N1(0) .
N(0)
N2(0)
N3(0)
t
• Life time critical point(s)
implies innovations, social and technological reforms
• Pace of life accelerates in next cycle
• Dynamics accelerates with net returns to scale (gama-rho)
Renew system conditions Potentially unstable point
Cycles duration decreases with N0
Cities accelerates with population
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Analogy with organism: Biologic vs. Social rhythms
Heart rate v/s mass Social rate vs. population
N= 100K => 4,04 km/hr
N= 1.000K => 4,13 km/hr (2,2%)
N= 10.000K => 4,23 km/hr (4,7%)
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Model Remarks
• Scale law emerges from: agents’ behavior, diversity and market conditions
• Diversity: creates super-linear dynamics
• Optimization: fundamental mechanism
• Resources and regulations: define constraints on choice sets and the final equilibrium
• Migrations: extension to a regional system
• The main result only needs bids distributed iid Fréchet and location equilibrium
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FROM URBAN DYNAMICS TO SUTAINABLE CITIES
1. STATITICAL EVIDENCE 2. THEORETICAL SUPPORT
3.RELEVANT IMPLICATIONS
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Implication Remarks
• Megacities capture returns to scale from: – Diversity: denies equity???
– Population: promote concentration ???
• Urban sustainability: – Potential instability
– Life time critical points
– Accelerated pace of life
CALL FOR LARGE SCALE RESEARCH ON ESTIMATING CURRENT CYCLE
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Provocative Remarks
• Organism metaphor: – nutrients-wealth
– cells-agents
HUMANS THINK, HUMANS ARE “FREE” …
SO THEY OPTIMIZE RESOURCES (time and material)
TO END UP FOLLOWING SIMILAR “NATURAL RULES”
ALTHOUGH SUPERLINEAR
GOOD NEWS: THEY ARE PREDICTABLE
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FREEDOM OF DEVELOPMENT
• Freedom of choice seems limited to “rational freedom” … i.e. to optimize
• Optimal choice induces scale laws of growth, innovation and economic and social costs
• Scale laws imply predictable development, at macro-scale and system cycles
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Phylosofical Remarks: long obsecions (Tzvetan Todorov, Les ennemies intimes de la démocratie, 2012)
• Helvetius (1758, Del espíritu) – “make a moral like an experimental physics”
• Condorcet (1743-1794) – all “human knowledge” may be converted into “objects of
mathematical science”.
– “the legislator is for the social order what the physicist is for nature”
We are far from understanding human behavior and its emerging (dis)order…
but maybe closer to do so,
and to harmonize it with nature