Understanding Urban Networks Through Accessibility
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Transcript of Understanding Urban Networks Through Accessibility
8/9/2019 Understanding Urban Networks Through Accessibility
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ERSA2005 – the 45th Congress of European Regional Science Assoc
August 2005, Vrije Universiteit Amsterdam
Understanding urban networks through acce
Jianquan Cheng, Frank Le Clercq and Luca Bertolin
AMIDST, University of Amsterdam, Amsterdam, Nieuwe Prinsengracht 130
1018 VZ, Amsterdam
The Netherlands
Tel: +31 020 525 2363
Fax: +31 020 525 4051
E-Mail: [email protected]
Abstract: The question to be investigated in the paper is how to c
networks, taking both place-bound activities and (quality of) transp
account. The description should help formulate planning ques
development of urban networks. Urban networks can mor
characterized as major nodes or concentrations of land uses in a g
Beyond this morphological description, places in the area can also be
the amount and diversity of activities to be accessed by means of a p
network. So, each place can be valued in terms of opportuniti
depending on its links to the transport network, the attractiveness o
given travel time or costs. The changes of activities at one place
workers or jobs) can thus, in combination with changes in the transp
travel speeds), influence the position of places elsewhere becaus
between places. The process of influence will be spatially diffused fu
that spatial competition is a hidden determinant of an urban network.
The paper will illustrate these different views of the urban network
part of the Randstad Holland conurbation (the greater Amsterdam a
different spatial representation. The comparisons between the patter
networks (morphological and opportunity based, or ‘virtual’) can
changing urban network, giving rise to planning questions such as:
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secondary centers and Amsterdam, and later to connect the regional
motorway grid. Today, with increasing specialization and the expan
in the intermediate zones, the challenge is rather the development of system and the introduction of hierarchies in the motorway syste
different cities, towns and major ex-urban activity concentrati
complementary centers in a more horizontal fashion.
The important question for the future of the city, then, is how its s
urbanity can remain connected within the networks of urban interac
which is partly
outside the traditional municipal boundaries. This gives rise to a new
Amsterdam will have to exchange its traditional ‘inside-out’ pol
expansion) for an ‘outside-in’ approach, where the focus shifts to po
the networks of multiple centres in a broader spatial field (Bertolini a
Built-up areas
Airport
Seaport
Railway
Motorway
Railway station
Fi ure 1. Amsterdam urban re ion with main infrastructure and sub c
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provides a unique combination of intercontinental air links and dir
the regional and national motorway and railway networks. The
become the focus of a rich and diverse concentration of activities conference, hotel, retail, and logistics). Other older and newer
increasingly the focus of specific concentrations. Large-scale office
financial and business services in particular, have been clustering ar
stations of Sloterdijk (for example, Teleport), Lelylaan (World
Amstel (Philips, Worldcom), Zuid (World Trade Center, the ABN-
banks). The area between Bijlmer station and the A2 motorway
preferred location for combined warehouse and office complexextremely dynamic information and communication technology (IC
among others, the European headquarters of Cisco). In these location
well as the availability of space, excellent access both to the regional
to metropolitan facilities including the airport. Urban centers elsewh
such the previously mentioned Almere or Zaanstad, are also experi
business locations, particularly as far as back offices are concerned.
small-scale professional services have, on the other hand, remaine
walking and cycling environment of the historic city center, which iideal breeding ground for up and coming Internet and multimedia bus
A similar differentiation may be also observed in the distribution o
most noticeably: new hospitals along the A10 motorway ring; the R
exhibition center, the Insurance Exchange, the District Tribuna
University around Zuid station; and a giant retail and leisure com
station. At the same time, more finely grained shopping, entertainm
activities have continued to thrive in the old city. Reinforcing th
unfortunate attempt at downtown-style office development betwee
1990s, a number of large cultural facilities have recently been o
opened along the southern IJ-river banks, east and west of Central St
In addition, and although the dynamism is somewhat more limited, re
(at least, of those who can choose!) also appear to be increasingly i
differences between, in addition to other factors, more and less acceless intensely used, urban areas. Furthermore, there are signs of an e
for high-quality apartments in the direct surroundings of the main mu
While interesting, the picture of the network sketched above is still h
and dependent on users’ perceptions. The method provide
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is globally similar but more continuous than that in figure 2. Or
spatially more segregated than inhabitants. Compared with figure 1
provide more accurate and detailed information for identifying cspatial relationships with the transport network, thus providing a
support to the morphological description of the previous section.
does not capture the functioning of the network as such, because the
between places of activity is not considered. Furthermore and relate
based representations of networks are not sensitive to changes in hu
spatial strategies, that is, they are of a static nature and as such not su
the dynamic changes in spatial and social interactions.
To illustrate both the potentials and the limits of a density-based repr
network, let us consider the example of the relationship between
supply of jobs, a crucial aspect of the functioning of urban network
can calculate the ratio of employment to inhabitants as in figure 4
help understand the spatial mismatch between inhabitants and em
location point of view, as it reflects the functional mixture at any
location. However, this information does not take the role of the trandetermining access to jobs and workers, into account, or the int
transport and land use. As a consequence, on the basis of such rep
impossible to assess how good a residential location is in terms of
business locations in terms of access to workers.
4. An accessibility-based view
It is a well-known common place that city is a complex system, mcomponents in spatial and temporal interactions. The pre-requisite t
planning is the scientific understanding of the complexity inherent in
studied. The complexity of a network is its interaction and the
interactions as a dynamic component. Interaction-based anal
theoretically better to understand the functions of a network. Bu
discussion in the previous section, here we take the issue of job a
example to illustrate its advantages.
Job accessibility is influenced by the complex social and spatial inte
land-use structure, transportation (e.g. availability of vehicles, existi
congestion in high-density areas), and the functional aspects of jobs
employment type, gender, age, education, their household roles an
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hour travel time. If the same calculation is made when incorporating
time decay, the difference between both results indicate whether i
include travel distance as a discriminating planning element in thinnetworks or, if no severe differences occur, it is just sufficient
locational pattern of jobs to inhabitants. The example can be
incorporation of other components, which might affect job oppo
competition for the same jobs executed by other inhabitants (compet
If this is overwhelming the distance effect, it might be more i
planning perspective to carefully plan the spreading of jobs to
worrying about travel distances in the urban network.
In this project, we adopt the strategy to model accessibility i
Figure 5. Illustration of components for job opportunity measure: [a): cdemand, by amount of workers; b): competitions in supply, by amount
c): distance decay in demand and supply; d): diversity of jobs]
a) b)
c) d)
i
j
i
j
i
j
i
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these components shows some aspect of the complex interactions wi
Figure 6 and 7 show the difference in spatial patterns of job o
application of the strategy of modelling. For example, the job aAmlere (right side in figure 6 and 7) is enhanced after incor
components of job accessibility, the same situation is also for the ci
Zaanstad. By contrast, the job access in the northern part of Amsterd
peripheral areas of other smaller cities is reduced and worse totally.
In contrast to the previous section, we can now adequately address
spatial relationship between job demand and supply in the netw
illustrate this, let us calculate the ratio of job opportunity (taking a
accessibility components) to the number of inhabitants as (b) in
accessibility-based ratio shows a remarkably different pattern with
based in (a) of figure 4. In figure 4, when using the same c
accessibility-based ratio implies a much stronger spatial mat
opportunity and inhabitants, which are expanded to the periphera
mainly because of the fact that job accessibility measure considered
transport and land use (employment, workers, and transport network)
The impacts of the different components of job accessibility can b
evaluated from figure 8. Comparing a, b, c and d in figure 8, the
change comes from the competitions on both demand and supply (i.e
jobs among workers and also competition for employees between
change in job opportunity is characterized by the increase in the s
Amsterdam city. The latter three maps (b, c and d) are globally si
changes in their spatial patterns. To identify the spatial (and planning
component, we calculate the ratio of job opportunity between any tw
job accessibility as figure 9, assuming other set of conditions unch
with a value greater than 1 means an increase of job opportunity an
than 1, conversely, means a decrease of job opportunity. The spati
ratio values could indicate different policy implications.
In the case of map a, the increase of job opportunity is clustered in and smaller) centers, this results from the spatial concentration of jo
or the density of jobs, which strengthens the competitive positio
demand (competition for jobs among workers).
In the case of map b, the change of job opportunity is largely d
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In the case of map d , the change of job opportunity is dominated by i
spatially distributed relatively more in the fringe than in the city
implies that, one the one hand, job diversity contribute less tcomponents, on the other hand, the job structure in Amsterdam c
significantly more diverse, compared with those in the fringe. P
structure resulted from the local policy of old-city preservation.
Linking figure 8 and 9, we can summarize that land use densific
mixture and job diversification can affect the level of job opportuni
the network, and thus the functioning of the network as a whole. Co
can be utilized as policy instruments within the framework of a n
strategy.
By taking Almere as example, the job opportunity there is limited a
heterogeneous (figure 7). Two reasons may contribute to this: one is
density of jobs, another is the relatively low functional mixture of job
Further elaborating the argument, figure 10-a illustrates what the imp
relocation of jobs from Amsterdam city center to Almere. Totallyrelocated in this example. The corresponding change of job opportu
in figure 10-b (where the impact of the change on all four com
accessibility is accounted for). This change results from the com
spatial interactions between various land uses, as linked by a tr
Similar examples could be made for the impacts of other land u
policies.
5. Implication for planning practice
It is well known that city is a complex system exhibited as a n
characterized with multiple actors, dynamic social interactions and
patterns. Any policy-making must be based on the proper unde
network. The Dutch national urbanisation policy currently in force i
inadequate and not a timely answer to societal changes (van der Bu2004). The illustration described above, by taking job accessibility
shows the importance of understanding such network from the func
just the morphological perspective. The latter is able to better reflec
the network. In the example of access to jobs, it shows how a c
workers at a location affects the level of opportunity at another locati
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can be helpful for the design of policy-making or strategy making. Th
will bring a new perspective to make sustainability-oriented po
practice. It is necessary to shift from physical sustainable to functiofrom an urban policy based on compactness to one considering
network. A functional, accessibility-based perspective on urban
network cities) points to a series of interesting questions for planni
as:
- What should be the planning aim for urban networks: mak
homogenous, more diverse or rather make them subject to (contro
developments?
- Improvements in the transport system may have more or less exog
the competitive position of urban places. How should these impacts
in transport planning?
- Are comprehensive planned (and controlled) interventions thi
networks, or are urban networks rather the outcome of adaptive
necessarily partial planning interventions, as those responding to tr
the need for urban expansion, changes in location preferences, etc.?
A discussion of these questions could help sketch a planning res
urban networks. This set of questions stems from the consideratio
discussed above call for an integrated approach to land use and tran
urban networks. Better policy coordination is indeed needed. Howe
policy coordination in urban networks must be also recognized. Ur
invariably highly fragmented in terms of public power, while the g
coordinating government and private decisions makes matters even mThe limits to policy coordination have also a temporal dimension.
show a wide range of paces of change: from the very long cycles
development, to the much shorter cycles of land use transfo
continuous adaptations in individual activity and mobility behavio
there are limits to just knowing what future developments will be. A
the need of improving coordination and reducing uncertainty, there
deal with the impossibility of coordination and the irreducibilityAccordingly, interventions that enhance the resilience and the adapta
use and transport system are needed (Bertolini, 2005). In order to ach
a need to continuously assess the potential implications of changes in
its appreciation by individuals and organizations, and to identify way
the ensuing development opportunities and threats. The ac
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Cheng, J., Bertolini, L., Clercq, F.L. and Kapoan, L., (2005
accessibility: a new strategy for its modeling. Journal of Transpor
review).
Handy, S. and Clifton, K.J., (2001) Evaluating neighborho
possibilities and practicalities. Journal of Transportation and Statistic
Mayer, I.S., Carton, L., de Jong, M., Leijten, M. and Dammers, E., (2
future of an urban network. Futures, 36: 311-333.
Smith, R.G., (2003) World city actor-networks. Progress in Human G
25-44.
van der Burg, A.J. and Dieleman, F.M., (2004) Dutch urbanisati
'compact city' to 'urban network'. Tijdschrift voor Economische en S
95(1): 108-116.
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F i g ur e 2 .P a t t e r n of e m pl o ym e n t d e n s i t y
F i g ur e 3 .P a t t e r n of p o p ul a t i on d e n s i t y
F
i g ur e 4 .R a t i o of e m pl o ym e n t ( a )
a n d o p p or t uni t y ( b ) t oi nh a b i t a n t s
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F i g ur e 6 . O p p or t uni t y wi t h o u t a n y c om p on e n t
F i g ur e 7 . O p p or t uni t y wi t h a l l c
om p on e n t s
F i g ur e 1 0 . C h
a n g e of j o b s ( a ) a n d c or r e s p on d i n
g c h a n g e of j o b o p p or t uni t y ( b )
a )
b )
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F i g ur e 8 . O p p or t uni t y , s t e p b y
s t e p ( a ) : c om p e t i t i on on d e m a n d ; b ) c om p e t i t i on s on d e m a n d a n d s u p pl y ; c ) : d i s t a n c e d e c a y ;
d ) j o b d i v e r s i t y
d )
c )
b )
a )
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F i g ur e 9 .R a t i o b e t w e e n t h e
v a r i o u s c om p on e n t s i n j o b o p p or t uni t y , s t e p b y s t e p ( a ) : a / o ; b ) b / a ; c ) c / b ; d ) d / c )
a )
b )
c )
d )