ANDRÉ OUREDNIK
MATHIS STOCK
JACQUES LÉVY
Chôros Lab
Swiss Fédéral Institute of Technology Lausanne

A major difficulty in measuring density indices lies in the fact that human individuals rarely spend all of their time in one single place. Such a mobility exists especially in societies that have opted for a functional diversification of the inhabited space, i.e., for the creation of a system of specialized places inducing individual mobility as a structural necessity. In the context of such societies, density indices calculated as numbers of residents divided by areas of the administrative units to which these residents are assigned seems highly biased. Density measurements in a society of mobile individuals must go beyond such a mono-topical reduction in order to account for the poly-topical character of any individual’s being-in-space. In our paper, we first give an account of the problems associated to density measurements in a society of mobile individuals.

Second, we describe a methodology aiming at taking this mobility into account. In this context, we define a density index that does not take into account the individuals themselves but rather the diverse amounts of time spent by any individual of a given population at any place. This index, which we call the “total stay-time density index” (TStDI), is the sum of these individual stay-times at any place. Finally, we present some results of the implementation of TStDI in our research on Swiss census data. Our research has revealed a considerable difference between residential and total stay-time densities, proving, above all, that the inconsideration of individuals’ mobility leads to underestimate central urban densities and to overestimate densities of peripheral spatial units.