  Measuring the degree of spatial spreading of a sample can be of great
interest when sampling from a spatial population. The commonly used spatial
balance index by Grafstr\"om et al. (2012) is particularly effective in
comparing the level of spatial spreading of different samples from the same
population. However, its unbounded and uninterpretable scale of measurement
does not allow to assess the level of spatial spreading in absolute terms and
confines its use to only raw comparisons. In this paper, we introduce a new
absolute measure of the spatial spreading of a sample using a normalized
version of the Moran's $I$ index. The properties and behaviour of the proposed
measure are analysed through two simulation experiments, one based on
artificial populations and the other on a population of real business units
located in the province of Siena (Italy).
