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histories”, those of the municipalities. The diversity of the municipal populations'
trajectories can also be analyzed (Figure 2.1(b)).
3) If the point is to understand the territory's dynamics as a process of exchange
between places, the dynamics of the department will be viewed as a process with
immigrations and emigrations. The aggregated trajectories of incoming or outgoing
inhabitants are then considered rather relevant: how many are gone, and where to?
And how many arrived, and where from? The population state at a given moment is
no longer envisaged as the result of a simple counting, the objective is to take
account of the direction of the migration flows of residents (Figure 2.1(c)). We are
then closer to a questioning about the processes. The flow becomes the object of
interest, characterized by an origin and a destination: this information existing at the
level of the municipality, it becomes an attribute of a “flow” object. These flows are
perdurant
entities.
Figure 2.1
.
Three points of view on spatial change
These examples illustrate the practical questions that the conception of empirical
objects raises relative to the dimensions of space and time: at what level do we want
to analyze change? What objects should be conceived as
endurant
(at what
geographical level should time be integrated)? What are the consequences of such
choices on data modeling and on the management of identities? Time may be
integrated at the object level (the duration of the existence), at the level of the
attributes (population at time
t
) or even in the form of events (for example, year of
transition from the status of rural municipality to urban municipality).
The result of this challenge is a database where empirical data are organized
according to a data model that derives from the conceptual model defined
beforehand. This database can be designed in an environment that includes or not a
language dedicated to the modeling of spatio-temporal data. Nevertheless, these two
aspects, object conceptualization and computing construction, should be considered
as two stages. The conceptualization may be envisaged independently of the second.
Indeed, it is fruitful to work it all through even if everything is not operationalized.
