For a given class F of closed sets of a measured metric space
(E,d,μ), we want to find the smallest element B of the class
F such that μ(B)≥1−α, for a given 0<α<1. This
set B \textit{localizes the mass} of μ. Replacing the measure μ by
the empirical measure μn gives an empirical smallest set Bn. The
article introduces a formal definition of small sets (and their size) and study
the convergence of the sets Bn to B and of their size