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.
La forme urbaine
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En provenance du cours de École Polytechnique Fédérale de Lausanne
Villes africaines I: Introduction à la planification urbaine
31 notes
École Polytechnique Fédérale de Lausanne
31 notes
À partir de la leçon
Le futur des villes ou comment planifier
Faire face au défi climatique qui change nos manières de faire la ville.
Rencontrer les enseignants
Jérôme ChenalDr
Faculté de l'Environnement Naturel, Architectural et Construit - ENAC
Hello, we are going to discuss density, urban form,
and compact cities of present day.
We are going to discuss what the English call "pattern".
And we are going to see what are the choices
that must be made when we want to design or plan the city.
There are three possibilities to fit into an existing urban structure.
Here is a city I'm drawing very quickly.
Here it is with a center.
Regardless, the first possibility is to actually intensify
the fringes, okay, to open, of course some new areas.
But we will try to build to the max the city within the city.
Second possibility, let me go back quickly to my drawing.
The second opportunity to implement, the city center is further intensified
by building the city within the city but on the outskirts
new areas are developed for the new future populations.
It can be just about anywhere but it is no longer desirable to have density
but rather a spread and then we continue to build the city like that.
Know that this is the drawing being used the majority of the time.
Finally, the third possibility is the creation
satellites, new and future centers
which then become, without doubt, the new centers of the future
that will maybe have to be intensified.
So there they are, the three ways
to arrive at being inserted into the existing urban structure.
Regardless of being by an intensification of the existing city,
or by an implementation in the outskirts of new plots of land,
or by multiplying the satellites, the city satellites.
The first solution is without a doubt the best one,
the one which we use 99% of the time is the second solution.
What is density?
Two possibilities.
It is the development density or population density.
Development density is not of great interest to us.
This is more of a day to day.
Why?
Because we realize that there are
changes in the social structures.
Already residents of cities today in African cities, the drawing where
three generations lived under one roof tends to gradually disappear.
Which means that there is a need for more housing
since each small entity, each generation,
needs its own housing.
Also the number of square meters attributed to
one housing unit per person tends to increase in the last decades.
We realize that with any number of
difficulties, economic crises that this notion can vary
relatively quickly but globally the number of square meters
available of housing per person is increasing.
Which means that for the same population
the number of households is increased
and the number of square meters per person is increased
which creates an explosion in built area.
This is the first densification, the development density.
But this is of no interest at all to us.
What interests in the case of an idea of a
a sustainable city which would be a compact city, a dense city,
is the population density which is expressed by number of people,
by thousands of people by hectare or square kilometer.
Some examples.
We see that density is expressed by resident per hectare
with Dhaka to Bangladesh 555 people per hectare
and then 64 per hectare in Paris.
So we see that between Los Angeles, extremely sparse,
Casablanca which has a very heavy density and Dhaka or Hon Kong which
have hyper densities, this is a way of urbanizing, a way of implementing
which is extremely different depending on the cities we come across.
Here is an example of low density.
We see that in fact to go from this plot of land
to these plots, we have a whole route so if we go back to the infrastructure,
the linear meter, the distance from the road compared to the number of inhabitants,
we see that it is very expensive to have low density.
On the other hand, high density like this has a number of advantages.
We are going to take a look at them, it's the compact city but also has,
but also has a number of disadvantages.
It's a great cost also, a concentration
of pollution, we have already discussed this.
And then we see in a drawing like this that the public space
is clearly absent and the quality of life therefore suffers.
So we see that between a low density and a high density,
there are advantages and drawbacks.
We will talk about the compact city, there is a current popular belief
which leans more in the direction of density.
It's important to know and I will draw the small diagram for you in the corner,
it's that we have both a hyper density which costs in energy
and a very low density which is equally very expensive in energy.
So between the two we have here an optimum which remains to be defined.
And the optimum of the first city is without doubt not the optimum
of city number two, and this optimum depends clearly on the morphology
of the city, the meteorological context, climate context particularly where
we will not have the same optimum
in the Sahelien cities as we do in the tropical cities.
So the advantages of the compact city
is an accessibility, facilitated of course.
These are relatively low infrastructure costs.
It is the possibility of preserving the natural resources since
we are going to arrange it in a dense way and then free other lands.
This facilitates social integration and to finish
a facilitation in the financial transactions since the people
are in co-presence, it's very easy to negotiate, to buy
to make a number of transactions from hand to hand.
The last point is the but.
But of course there is always an but
and this compact city we have already said it
with high densities, there are a number of
water waste management problems, of pollution management.
Let's keep in mind that we have to have
an arbitration between the nebulous city and the compact city.
And we have to take into account all the evaluation criteria.
In regards to the accessibility issues, it's of course the compact city.
In regards to climate change issues, it's not necessarily
the compact city which best resists to the climate change effects.
Another congruent element with density, with the urban form,
is the issue of mixing and that of diversity.
Mixing, it can be social, it can be functional.
Urban history indicates to us that social mixing often comes from
a sociologist fantasy since there are only very few
moments in the global urban history where populations
have not been clearly separate and where there has been total mixing.
So the mixing is more or less great.
The extreme cases being apartheid
but w realize that the implementations of the richest
with those of the poorest don't take place
in the cities and this social mixing
which is an empty promise is extremely difficult
to put in place and the examples of
urban history are there more so to show us
that it is not possible to put in place.
On the other hand, functional mixing, this is very easy to put in place.
What is it?
It's that we don't have a neighborhood
that's only residential, a neighborhood that's only business,
but that we have a big neighborhood
that is both business and residential.
And that is what we advocate.
The African cities are by definition, mixed cities, they have
a functional mixing, this is what we need to try and maintain and keep at all costs.
When we have created the urban form, when we have chosen low density
or high density, when we have begun
to draw, future needs must be anticipated.
We are not going to draw the final form today.
We must imagine that what we are drawing today is only a step and that
we will know the final form in 10, 20, 50 or 100 years or never but that
what we do today is but a first step
and as a result,
we must absolutely anticipate what we will need tomorrow
so that the urban form may be able to continue allowing
the implementation of needs in services or infrastructures.
But it's of no use to just provide a parcel for future installation.
The plot must still be secured.
In how many cities have we seen subdivisions which have been built
on plots that were for the construction of a hospital or a school.
So we must be able to then secure the parcels
that have been identified for future needs.
And finally when we discuss urban forms, we are referring to drawings
of urban forms and we are discussing the need for drawing public space.
Public space has become the poor parent of the city and it's exactly
through public space that the city must recreate and redraw itself.
So let's turn our attention to the drawing itself, to the form
of public space, to the spatiality that we are going to give it.
If we look at the big cities, the big urban models,
the cities which win throughout the world, the cities which are
taken as examples, you can see from London to New York, from Singapore
to Zurich, you can all that all these cities have made an effort.
The case of Barcelona is very interesting for this.
All of these cities have made an effort for public space.
And it's through this public space, an space open to all,
that we will be able to recreate the city of tomorrow.
So there it is for the issues regarding pattern.
We are between the planning and the design.
The English divide urban planning and urban design.
We have a tendency in the francophone world
to not separate them and to use the same ways to react.
I think that it's necessary to see if we are discussing
at a territorial and strategic level or if we are discussing
a large scale project, about city design
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