Le cours permet d'apprendre les bases de la planification urbaine à travers ses dimensions techniques, environnementales, sociales, économiques et symboliques. Le cours parle uniquement des villes africaines et même si celles-ci ont valeurs d'exemple pour les ville du Sud, voire toutes les villes, nous nous efforçons à remettre les problématiques dans un contexte africain.
L'étalement urbain
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Из курса от партнера École Polytechnique Fédérale de Lausanne
Villes africaines I: Introduction à la planification urbaine
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École Polytechnique Fédérale de Lausanne
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La planification et ses outils
La ville se finance, elle demande des ressources qui s'obtiennent par des biais divers.
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Jérôme ChenalDr
Faculté de l'Environnement Naturel, Architectural et Construit - ENAC
This week we are in Cameroon, in the capital.
So welcome, all participants to Yaoundé.
Briefly, in this video we'll discuss what is urban sprawl.
Urban sprawl is considered, rightly or wrongly,
as a form of urban dysfunction.
It is when the city outgrows its own administrative borders.
We speak of urban sprawl when a city begins to grow and spread
like oil stains, all over the place, beyond its administrative borders
Logically, the master plan should fix urban sprawl,
should establish the limits beyond which it is no longer possible to build.
Urban sprawl is when a city spreads throughout,
in all the gaps and spaces, even those most dangerous.
In other words, one of the principal effects of urban sprawl
is that it destroys natural resources.
So we seek out land further and further out,
for land virgin of all urbanization.
But urban sprawl is also where we have intrusion
in places were one simply should not build.
In ravines, in ditches.
And in the end it establishes itself in zones we call non-edificandi,
which are zones where one absolutely should not build.
Why? Because it's dangerous, or because it's a nature reserve,
or because there are specific resources,
this can be a groundwater table, or water resources, a lake,
this can be a marsh, a certain type of prairie,
a certain type of forest where there are protected species.
But urban sprawl not only poses problems
in terms of resources or non-building zones,
it poses problems in terms of infrastructure.
The greater the sprawl, the growth,
the farther the city grows from its center,
the more difficult it is to set up the necessary networks.
The less dense the city, the more diffuse it is,
the more expensive the linear meter of pipe per capita,
or the greater the number of pipes or networks per capita.
So one of the important effects of urban sprawl is, finally,
that it does not allow us to service and sustain the entire area.
And the greater the sprawl,
the fewer the networks available for all these surfaces.
We were speaking of networks,
but its exactly the same with transportation systems.
The farther away I go, the farther it is to reach me,
or the farther I must go to bring them to the center.
But the question of networks or of transportation systems,
is exactly and strictly the same.
So what are the causes of this urban sprawl?
A legal question,
a legal case which, ultimately, doesn't exist, for it is allowed.
And if it exists, it is not applied.
Or if one tries to apply the law one simply doesn't have the means
to control its application.
It's not enough to just say, "This is the regulation, this is the law."
There must also be entire units of code enforcers whose job it is to ensure
that what is put in the law is truly applied on the ground.
The problem in most cities is that the legislative infrastructure exists,
but the means to control it do not, and as we know, without its control
people will continue to spread out as they wish,
with or without the law's approval.
Beyond the existing regulation there are urban plans
which are, in principle, extremely outdated.
These are rarely updated, and even when they are, they are rarely utilized.
We'll examine the limits of these plans,
and how to overcome these limits, in the videos which follow.
For now let's keep in mind that the plan is rarely as it should be,
is rarely as useful as it should be,
but it should, normally, be able to contain this urban sprawl,
because it should define the perimeter within which one can develop,
and the perimeter beyond which one cannot.
Another cause of urban sprawl
is clearly that demand exceeds supply.
This is why people will go farther and farther out.
In a free land market, in a free housing market,
in a liberal economic system price is determined
as a function of a certain number of contextual criteria,
but in principle as a function of supply and demand.
So if I wish to construct, to own land, I must go as far as possible
because the prices, in the center of the city, are beyond my reach.
Because of this people go farther and farther out.
And the denser I make the center,
the more I develop its infrastructure, its networks,
the higher the price of the land,
and the farther away the poorest must go to find affordable land.
This is one of the phenomena, one of the causes of urban sprawl.
Now that we've seen its causes,
let's look at how we might reduce its effects.
First and foremost we must put in place
a legal framework, one which is relatively simple,
yet operational, and one must provide it with means of control.
We must determine a certain number of non edificandi zones,
and implement strict controls, physical controls over the land,
so that no one can settle in the zones,
which might be zones with ravines, zones which could be dangerous,
whether due to flooding, because of marshlands,
because of sandstorms, or on dunes which can shift.
This is one of the first points, to put in place a legal framework,
correctly, simply, which may well exist, but as we've seen, but above all
it must clearly be able to control this framework.
And parallel to this, it is not just a matter of saying
this is authorized, this is prohibited.
There must be a series of measures which accompany this.
And if one does not look into the question of housing,
if one does not propose aids in supply, and demand, when it comes to housing.
If there is not a public housing policy
which enables even the poorest to gain access to land,
urban sprawl will continue.
So at the same time act within a framework strictly of planning,
regulatory, judicial, and their different forms of control,
and at the same time on public policy, most notably housing and development.
If we do not address both aspects,
urban sprawl will continue now, and forever.
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