  We study in detail the properties of clusters of ultra high energy cosmic ray
events, looking in particular to their angular correlation function, to the
relative frequency of clusters with different multiplicities (e.g. doublets vs.
triplets or quadruplets), as well as the way in which these quantities should
evolve for different ultra high energy cosmic rays source scenarios as a
function of the experimental exposure achieved. We identify some useful tools
which can help to characterise the nature of the cosmic ray sources in a more
precise way after a modest increase in statistics will be achieved in the very
near future, even before strong signals from individual sources become
eventually observable.
