  Two dimensional velocity fields have been an important tool for nearly 30
years and are instrumental in understanding galactic mass distributions and
deviations from an ideal galactic disk. Recently a number of new instruments
have started to produce more detailed velocity fields of the disks and nuclear
regions of galaxies. This paper summarizes some of the underlying techniques
for constructing velocity fields and deriving rotation curves. It also urges to
simulate observations from the data-cube stage to reject subtle biases in
derived quantities such as rotation curves.
