  We discuss the crucial role played by finite-size effects and inhomogeneity
on the Beresinkii-Kosterlitz-Thouless (BKT) transition in two-dimensional
superconductors. In particular, we focus on the temperature dependence of the
resistivity, that is dominated by superconducting fluctuations above the BKT
transition temperature $T_{BKT}$ and by inhomogeneity below it. By means of a
renormalization-group approach we establish a direct correspondence between the
parameter values used to describe the BKT fluctuation regime and the distance
between $T_{BKT}$ and the mean-field Ginzburg-Landau transition temperature.
Below $T_{BKT}$ a resistive tail arises due to finite-size effect and
inhomogeneity, that reflects also on the temperature dependence of the
superfluid density. We apply our results to recent experimental data in
superconducting LaAlO$_3$/SrTiO$_3$ heterostructures, and we extract several
informations on the microscopic properties of the system from our BKT fitting
parameters. Finally, we compare our approach to recent data analysis presented
in the literature, where the physical meaning of the parameter values in the
BKT formulas has been often overlooked.
