  At any instant, there are roughly 1000 ongoing microlensing events to sources
brighter than 20th magnitude in the Milky Way Galaxy. Large-scale maps of the
microlensing optical depth and the mean timescale are constructed for a number
of models of the Galactic bar and disk, incorporating the effects of streaming
and spiral structure. Freudenreich's model can reproduce the high optical
depths towards the Bulge. It is also in good agreement with the data towards
the spiral arms (except for the gamma Norma field). Spiral structure tends to
increase the optical depth by about 20% and the mean timescale by about 100%.
Different bar morphologies give characteristically different shaped contours,
especially at low Galactic latitudes (|b| < 2 degrees). These could be traced
out with a K band microlensing survey, consuming about 100 minutes per night on
a telescope like VISTA.
