  We present here a fast code for creating a synthetic survey of the Milky Way.
Given one or more color-magnitude bounds, a survey size and geometry, the code
returns a catalog of stars in accordance with a given model of the Milky Way.
The model can be specified by a set of density distributions or as an N-body
realization. We provide fast and efficient algorithms for sampling both types
of models. As compared to earlier sampling schemes which generate stars at
specified locations along a line of sight, our scheme can generate a continuous
and smooth distribution of stars over any given volume. The code is quite
general and flexible and can accept input in the form of a star formation rate,
age metallicity relation, age velocity dispersion relation and analytic density
distribution functions. Theoretical isochrones are then used to generate a
catalog of stars and support is available for a wide range of photometric
bands. As a concrete example we implement the Besancon Milky Way model for the
disc. For the stellar halo we employ the simulated stellar halo N-body models
of Bullock & Johnston (2005). In order to sample N-body models, we present a
scheme that disperses the stars spawned by an N-body particle, in such a way
that the phase space density of the spawned stars is consistent with that of
the N-body particles. The code is ideally suited to generating synthetic data
sets that mimic near future wide area surveys such as GAIA, LSST and HERMES. As
an application we study the prospect of identifying structures in the stellar
halo with a simulated GAIA survey. We plan to make the code publicly available
at http://galaxia.sourceforge.net.
