  The arrival direction distribution of cosmic ray particles observed on Earth
is shaped by the cumulative effects of their galactic source locations and of
trajectory bending in the turbulent interstellar magnetic field. Coherent
magnetic structures are expected to disrupt particle trajectories and their
observed distribution, as well. The heliosphere, the large magnetic bubble
generated by the sweeping effect of solar wind on the local interstellar
plasma, strongly affects the TeV cosmic ray particles detected on Earth. By
unfolding the heliospheric influence on the observed anisotropy, it is possible
to determine the pitch angle distribution of cosmic rays in the interstellar
medium. This information makes it possible to study in detail the global
diffusion properties of TeV cosmic rays in the Galaxy. However, observational
blindness to key features of the cosmic ray arrival direction distribution may
lead to biases in the determination of the heliospheric influence and of the
interstellar CR distribution. Any inference of galactic TeV CR diffusion
properties must carefully account for local propagation phenomena and
observational limitations.
