Geoscience Reference
In-Depth Information
the city is a complex object for which there are several definitions, and whose
definition is evolved over time. The set of cities studied is that of the European
cities. The objective is to build a coherent database to then analyze the different
dynamics of the cities relatively to indicators based on population statistics
(employment rate, capacity to attract as a labor market, activity rates etc...).
The issues raised by following up cities as “objects” on a long period of time of
two centuries, while integrating the functional changes of these objects, have already
been presented in Chapter 1. In this example, the focus is placed on the challenges
that the construction of a database about cities at an international level raises; that is
to say, the challenges of harmonization are not in time here, but in space. Indeed,
each country has its own definition, its own administrative level of statistics
collection (census, survey and civil status) and the definition of cities is submitted to
evaluations based on national statistics. The city is here considered solely in its
morphological definition that is based on the continuity of the built area. The first
stage consists of assessing the spatial envelope associated with this definition, for
each city and each date. The second stage consists of evaluating the associated
semantic attributes, knowing that they come from different statistical sources that
correspond to administrative elementary entities, the local administrative unit level 2
(LAU2)
8
. These various statistics (resident population, active population, employed
population, etc.) will have to be “transferred” through a model of aggregation or
disaggregation at the level of the envelope defined by the continuity of the built
area. The third step will consist of testing the construction method of the entities in
time, and assessing the consistency of the
endurant objects
constructed that way.
If the example of the morphological city is finally a classical example from a
geomatics point of view, the fact of raising it in an international context renews this
question. For the construction of international databases, two types of approaches
can be mobilized: a
bottom-up
approach that consists of building an international
database from the national databases, by integration of the different national
specifications; a
top-down
method that consists of building an international database
from a common source existing at the European level and in deriving the same
specifications (Figure 2.4). In the
bottom-up
approach, we will firstly rely on
national databases (Figure 2.4(a)) that define the agglomeration on the basis of an
aggregation of elementary administrative entities, the LAU2, according to a
continuity criterion of the built area evaluated in most cases by photointerpretation.
The construction of a database at the international level would require aligning the
specifications of the national databases and evaluating the equivalences in order to
8 The LAU2 corresponds to the second level of the administrative nomenclature established
by Eurostat for the totality of the European countries. This corresponds, for example, to
“municipalities” in France, to wards in the United Kingdom,...
