Geoscience Reference
In-Depth Information
- in absolute terms, the evolution of the urban system is characterized by an
overall growth, all the cities registering a growth of their population;
- in relative terms, i.e. by relating, for example, the population of each city to the
population of the largest city, the representation underlines a growth concentration
process at the top of the urban hierarchy (Figure 3.4(a)).
The evolution of the populations of Nimes and Montpellier offers another
example (Figure 3.4(b)). The representation of the populations in relative values
(compared to the total of the urban population of the region) allows the discontinuity
occurring since the 1960s between the population trajectories of the two cities to be
highlighted.
Figure 3.4.
The issue of the referential in the change analysis
(source [ARC 98] (revised L. Lizzi))
The question of the referential may also arise at the level of the involved
methods. Let us suppose that the interest is about the follow-up over time of a spatial
organization. In a “snapshot”-based approach, the same static model is used at each
date as a grid of interpretation of the spatial configuration (calculation of a spatial
autocorrelation coefficient at each date, for example). Each result will be an element
of the trajectory describing the evolution of the structure (here a spatial
autocorrelation coefficient trajectory). If the method depends on parameters (in the
case of spatial autocorrelation, this would be the adjacency graph for example) the
