  The organization of the electrons in the ground state is classified by means
of topological invariants, defined as global properties of the wavefunction.
Here we address the Chern number of a two-dimensional insulator and we show
that the corresponding topological order can be mapped by means of a
"topological marker", defined in $\r$-space, and which may vary in different
regions of the same sample. Notably, this applies equally well to periodic and
open boundary conditions. Simulations over a model Hamiltonian validate our
theory.
