  The information extracted from large galaxy surveys with the likes of DES,
DESI, Euclid, LSST, SKA, and WFIRST will be greatly enhanced if the resultant
galaxy catalogues can be cross-correlated with one another. Predicting the
nature of the information gain, and developing the tools to realise it, depends
on establishing a consistent model of how the galaxies detected by each survey
trace the same underlying matter distribution. Existing analytic methods, such
as halo occupation distribution (HOD) modelling, are not well-suited for this
task, and can suffer from ambiguities and tuning issues when applied to
multiple tracers. In this paper, we take the first steps towards constructing
an alternative that provides a common model for the connection between galaxies
and dark matter halos across a wide range of wavelengths (and thus tracer
populations). This is based on a chain of parametrised statistical
distributions that model the connection between (a) halo mass and bulk physical
properties of galaxies, such as star-formation rate; and (b) those same
physical properties and a variety of emission processes. The result is a
flexible parametric model that allows analytic halo model calculations of
1-point functions to be carried out for multiple tracers, as well as providing
semi-realistic galaxy properties for fast mock catalogue generation.
