  Moir\'e superlattices can induce correlated-electronic phases in twisted
van-der-Waals materials. Strongly correlated quantum phenomena emerge, such as
superconductivity and the Mott-insulating state. However, moir\'e superlattices
produced through artificial stacking can be quite inhomogeneous, which hampers
the development of a clear correlation between the moir\'e period and the
emerging electrical and optical properties. Here we demonstrate in
twisted-bilayer transition-metal dichalcogenides that low-frequency Raman
scattering can be utilized not only to detect atomic reconstruction, but also
to map out the inhomogeneity of the moir\'e lattice over large areas. The
method is established based on the finding that both the interlayer-breathing
mode and moir\'e phonons are highly susceptible to the moir\'e period and
provide characteristic fingerprints. We visualize microscopic domains with an
effective twist-angle resolution of ~0.1{\deg}. This ambient non-invasive
methodology can be conveniently implemented to characterize and preselect
high-quality areas of samples for subsequent device fabrication, and for
transport and optical experiments.
