Calibrated and completeness-corrected optical stellar density maps of
  the Northern Galactic Plane
  Following on from the second release of calibrated photometry from IPHAS, the
INT/WFC Photometric H-alpha Survey of the Northern Galactic Plane, we present
incompleteness-corrected stellar density maps in the r and i photometric bands.
These have been computed to a range of limiting magnitudes reaching to 20th
magnitude in r and 19th in i (Vega system), and with different angular
resolutions -- the highest resolution available being 1 square arcminute. The
maps obtained cover 94 percent of the 1800 square-degree IPHAS footprint,
spanning the Galactic latitude range, -5{\deg} < b < +5{\deg}, north of the
celestial equator. The corrections for incompleteness, due to confusion and
sensitivity loss at the faint limit, have been deduced by the method of
artificial source injection. The presentation of this method is preceded by a
discussion of other more approximate methods of determining completeness. Our
method takes full account of position-dependent seeing and source ellipticity
in the survey database. The application of the star counts to testing reddened
Galactic disc models is previewed by a comparison with predicted counts along
three constant-longitude cuts at l $\simeq$ 30{\deg}, 90{\deg} and 175{\deg}:
some over-prediction of the most heavily reddened l $\simeq$ 30{\deg} counts is
found, alongside good agreement at l $\simeq$ 90{\deg} and 175{\deg}.
