Estimate density of F-stars as a fn of (RA, Dec)

To get a feel for how many spectrophotometric standards we have across the HSC footprint, we collect stars from the HSC database and apply magnitude + color cuts to select F-stars and estimate their spatial density.  The density is of course dependent on the cuts we apply, but it would be useful to get a feel at this point and also to setup a machinery to estimate the stellar density for a given set of mag + color cuts.