  We deal with the orbit determination problem for a class of maps of the
cylinder generalizing the Chirikov standard map. The problem consists of
determining the initial conditions and other parameters of an orbit from some
observations. A solution to this problem goes back to Gauss and leads to the
least squares method. Since the observations admit errors, the solution comes
with a confidence region describing the uncertainty of the solution itself. We
study the behavior of the confidence region in the case of a simultaneous
increase of the number of observations and the time span over which they are
performed. More precisely, we describe the geometry of the confidence region
for solutions in regular zones. We prove an estimate of the trend of the
uncertainties in a set of positive measure of the phase space, made of
invariant curve. Our result gives an analytical proof of some known numerical
evidences.
