  Using redshifts as a proxy for galaxy distances, estimates of the 2D
transverse peculiar velocities of distant galaxies could be obtained from
future measurements of proper motions. We provide the mathematical framework
for analyzing 2D transverse motions and show that they offer several advantages
over traditional probes of large scale motions. They are completely independent
of any intrinsic relations between galaxy properties, hence they are
essentially free of selection biases. They are free from homogeneous and
inhomogeneous Malmquist biases that typically plague distance indicator
catalogs. They provide additional information to traditional probes which yield
line-of-sight peculiar velocities only. Further, because of their 2D nature,
fundamental questions regarding vorticity of large scale flows can be
addressed. Gaia for example is expected to provide proper motions of at least
bright galaxies with high central surface brightness, making proper motions a
likely contender traditional probes based on current and future distance
indicator measurements.
