  This paper uses the theory of point processes and stochastic geometry to
quantify the sky visibility experienced by users located in an urban
environment. The general idea is to represent the buildings of this environment
as a stationary marked point process, where the points represent the building
locations and the marks their heights. The point process framework is first
used to characterize the distribution of the blockage angle, which limits the
visibility of a typical user into the sky due to the obstruction by buildings.
In the context of communications, this distribution is useful when users try to
connect to the nodes of an aerial or non-terrestrial network in a Line-of-Sight
way. Within this context, the point process framework can also be used to
investigate the gain of connectivity obtained thanks to Reconfigurable
Intelligent Surfaces. Assuming that such surfaces are installed on the top of
buildings to extend the user's sky visibility, this point process approach
allows one to quantify the gain in visibility and hence the gain in
connectivity obtained by the typical user. The distributional properties of
visibility-related metrics are cross-validated by comparison to simulation
results.
