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:



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



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



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



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



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



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



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



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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understanding urban networks through accessibility

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