  We examine the errors on counts in cells extracted from galaxy surveys. The
measurement error, related to the finite number of sampling cells, is
disentangled from the ``cosmic error'', due to the finiteness of the survey.
Using the hierarchical model and assuming locally Poisson behavior, we
identified three contributions to the cosmic error:
  The finite volume effect is proportional to the average of the two-point
correlation function over the whole survey. It accounts for possible
fluctuations of the density field at scales larger than the sample size.
  The edge effect is related to the geometry of the survey. It accounts for the
fact that objects near the boundary carry less statistical weight than those
further away from it.
  The discreteness effect is due to the fact that the underlying smooth random
field is sampled with finite number of objects. This is the ``shot noise''
error.
  Measurements of errors in artificial hierarchical samples showed excellent
agreement with our predictions. The probability distribution of errors is
increasingly skewed when the order $N$ and/or the cell size increases. The
Gaussian approximation is valid only in the weakly non-linear regime, otherwise
it severely underestimates the true errors. We study the concept of ``number of
statistically independent cells'' This number is found to depend highly on the
statistical object under study and is generally quite different from the number
of cells needed to cover the survey volume. In light of these findings, we
advocate high oversampling for measurements of counts in cells.
