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fractal features of the “sprawling” urban patterns, makes for easy access to open
landscape, since green pockets enter into urbanized areas and may be a useful goal
for planning (Fig. 2.10 c), unlike the usual tendency to round off urban borders as
was made evident for the teragon!
Looking at the dimension values for agglomerations (Tables 2.1 and 2.2 ), we see
that fractal dimension of about 1.5-1.7 corresponds to urban fabrics with rather
contrasted patterns resembling the constructed fractal of Fig. 2.4 b. In Walloon
examples, dimensions were even lower.
Comparing schema, Fig. 2.1 b-c shows not only that fractal patterns save
larger patches from urbanization but illustrates another important feature about
accessibility. We may imagine that the nodes of the fractal networks correspond to
service centers of various ranks. Hence, all nodes can be considered as providing
facilities for daily needs; the four larger peripheral nodes can be interpreted as
centers also offering shopping and services amenities for weekly frequency of
recourse. Finally, the main center concentrates all types of amenities, also those
called on more rarely. Indeed, the less often amenities are frequented; the better
users accept long trips. This type of reasoning is reminiscent, of course, of central
place theory. Different authors emphasize the importance of developing secondary
centers or polycentric urban networks (Fouchier 1995 ). This is, e.g., discussed in
the frame of Calthorpes' concept of “New Urbanism” (Calthorpe 1993 )inorderto
minimize trip lengths. Of course, investigations have shown that consumers choose
not always closest shopping facilities (Clark 1968 ) but this is also due to the fact that
car accessibility has been improved over a long time and fuel costs were low. This
is why we introduce in the following a poorly linked public transportation network
avoiding direct concurrence between shopping areas providing the same type of
offer. Of course, street network should be conceived in the same sense avoiding
high-quality links between subcenters of same level.
Central place theory has also been criticized for other reasons often referring
to real-world situation which seems in many cases not in coherence with this
model (Berry and Pred 1961 ). But this does not exclude that for planning, the
basic principle of a planning model based on a hierarchical principle taking into
account the frequency of recourse can be useful and remains a reference in planning
essentially in German speaking countries. Weichhart et al. ( 2005 ) underline the
“naturalness” of this approach.
However, unlike in Christallers' central place theory, in the proposed spatial
system, the cities here are not distributed uniformly in space but concentrated near
transportation routes, meaning green areas can be saved from urbanization. Hence,
this type of spatial arrangement turns out to be even more efficient than the purely
axial development models.
Interpreting the nodes of the transportation network as sites concentrating
shopping and service amenities, the concept is similar to that of the “transit-oriented
development” suggested by Calthorpe ( 1993 ), but the mix of open landscape and
urbanized zones is reminiscent also of the debate about the Zwischenstadt of
Sieverts ( 1997 ) or the reflections of Dubois-Taine and Chalas ( 1997 ) about the ville
émergente .
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