  We propose a framework that connects the spatial symmetries of a metasurface
to its material parameter tensors and its scattering matrix. This provides a
simple yet effective way to effortlessly determine properties of a metasurface
scattering response, such as chirality or asymmetric transmission, and which of
its effective material parameters should be taken into account in the prospect
of a homogenization procedure.
  In contrast to existing techniques, this approach does not require any a
priori knowledge of group theory or complicated numerical simulation schemes,
hence making it fast, easy to use and accessible. Its working principle
consists in recursively solving symmetry-invariance conditions that apply to
dipolar and quadrupolar material parameters, which include nonlocal
interactions, as well as the metasurface scattering matrix. The overall process
thus only requires listing the spatial symmetries of the metasurface.
  Using the proposed framework, we demonstrate the existence of multipolar
extrinsic chirality, which is a form of chiral response that is achieved in
geometrically achiral structures sensitive to field gradients even at normal
incidence.
