  The local invariants of a meromorphic quadratic differential on a compact
Riemann surface are the orders of zeros and poles, and the residues at the
poles of even orders. The main result of this paper is that with few
exceptions, every pattern of local invariants can be obtained by a quadratic
differential on some Riemann surface. The exceptions are completely classified
and only occur in genera zero and one. Moreover, in the case of a nonconnected
stratum, we show that, with three exceptions in genus one, every invariants can
be realized in each connected component of the stratum. These results are
obtained using the flat metric induced by the differentials. We give an
application by bounding the number of disjoint cylinders on a primitive
quadratic differential.
