  Riemann's non-differentiable function is a classic example of a continuous
function which is almost nowhere differentiable, and many results concerning
its analytic regularity have been shown so far. However, it can also be given a
geometric interpretation, so questions on its geometric regularity arise. This
point of view is developed in the context of the evolution of vortex filaments,
modelled by the Vortex Filament Equation or the binormal flow, in which a
generalisation of Riemann's function to the complex plane can be regarded as
the trajectory of a particle. The objective of this document is to show that
the trajectory represented by its image does not have a tangent anywhere. For
that, we discuss several concepts of tangent vectors in view of the set's
irregularity.
