  A technique of ``approximate group analysis'' recently developed by Baikov,
Gazizov and Ibragimov is applied to a differential approximation (otherwise
referred to as an equivalent differential equation) corresponding to the finite
difference approximation of a nonlinear advection equation on unstructured
grid. We determine which groups from the infinite variety of groups admitted by
a nonlinear advection equation ``survive'' the discretization. The situations
arising for different choices of an arbitrary function (local speed of
propagation) are also studied.
