  The Milky Way is a barred spiral galaxy, with physical properties inferred
from various tracers informed by the extrapolation of structures seen in other
galaxies. However, the distances of these tracers are measured indirectly and
are model-dependent. We constructed a map of the Milky Way in three-dimensions
based on the positions and distances of thousands of classical Cepheid variable
stars. This map shows the structure of our Galaxy's young stellar population,
and allows us to constrain the warped shape of the Milky Way's disk. A simple
model of star formation in the spiral arms reproduces the observed distribution
of Cepheids.
