For every Borel set , let
be its random point count. A Non-homogeneous Poisson point process with intensity function of a point process is characterized by:
Because has a density with respect to Lebesgue measure, it is atomless, so the process is simple: almost surely no location occurs more than once.
A Non-homogeneous Poisson point process with intensity function is a random counting measure such that, for every finite family of pairwise disjoint bounded Borel sets , the counts are independent random variables and
The assumed local integrability makes each Poisson parameter finite. This count law and independence characterize the process.