  Several measurements of QSO-galaxy correlations have reported signals much
larger than predictions of magnification by large-scale structure. We find that
the expected signal depends stronly on the properties of the foreground galaxy
population. On arcminute scales it can be either larger or smaller by a factor
of two for different galaxy types in comparison with a linearly biased version
of the mass distribution. Thus the resolution of some of the excess
measurements may lie in examining the halo occupation properties of the galaxy
population sampled by a given survey; this is also the primary information such
measurements will provide.
  We use the halo model of clustering and simulations to predict the
magnification induced cross-correlations and errors for forthcoming surveys.
With the full Sloan Digital Sky Survey the statistical errors will be below 1
percent for the galaxy-galaxy correlations and significantly larger for
QSO-galaxy correlations. Thus accurate constraints on parameters of the galaxy
halo occupation distribution can be obtained from small scale measurements and
on the bias parameter from large scales. Since the lensing induced
cross-correlation measures the first moment of the halo occupation number of
galaxies, these measurements can provide the basis for interpreting galaxy
clustering measurements which measure the second and higher order moments.
