Geoscience Reference
In-Depth Information
1) What is the evolution of the percentage of the working population residing in
municipality A and working in municipality B?
2) What is the evolution of the recruitment area of the employment center C?
(i.e. what are the series of municipalities of which part of the residents are working
in the employment center C?)
It is obvious that in this exploration of change, the temporal dimension is at the
heart of the questioning as it is of the formalization that allows exploring it. If
“physical” time is linear [KLE 07], the temporal phenomenon that we observe may
appear cyclical (repeating on a regular basis): using a misnomer, we speak of cyclic
time. In fact, it corresponds to the way in which we need to formalize the temporal
dimension, in order to allow the transition from a linear interpretation of time to a
cyclic interpretation. In this case, the granularity of the cycle must be precised. For
example, the question “what is the distribution of shops' frequentation during
weekdays?” implies that the formalization of time integrates the days of the week.
Only in this case, a calculus of accumulation or of average of visits per day, is
possible. Other time forms can be envisaged, corresponding once again to other
representations of the temporal phenomenon [WOR 05].
These first explorations “view” the data, but they have also another role: they
allow us to test the way in which the empirical observations have been implemented
and the way in which the objects have been conceptualized and identified in their
3Ds and in their various relationships. We will not exemplify further the exploration
of the relationships' dynamics here, whether they concern composition or interaction
relationships. The composition relationships (composition of a city in terms of
census tracts or composition of a landscape in terms of landscape features) will be
illustrated in the examples at the end of this chapter. Analysis of interactions'
relationships (material or immaterial exchanges between places) will be processed in
the following chapters.
Each of these queries will be able to target either an object or a group of objects,
or either a synthesis of a group of objects: we re-encounter the idea of interpretation
levels recommended by Bertin [BER 67], the elementary level and top level. When
the query targets a group of objects, it will be necessary to use aggregation functions
to obtain a synthetic view. These interpretation levels exist for each of the 3Ds. The
question may target an object or several objects, a moment or a period, a place or a
set of places, an attribute value or one or several intervals. We call the result of a
query, a view which, depending on the case may be tabular, graphical or
cartographic. If the chosen level is the elementary level on each of the dimensions,
the query will produce a view of the raw data (the densities' evolution of a given
municipality over all the period's dates). If the general level is chosen for one of the
dimensions, it will give rise to a calculation which synthesizes the group of objects
