  The VST Photometric Halpha Survey of the Southern Galactic Plane and Bulge
(VPHAS+) is surveying the southern Milky Way in u, g, r, i and Halpha at 1
arcsec angular resolution. Its footprint spans the Galactic latitude range -5 <
b < +5 at all longitudes south of the celestial equator. Extensions around the
Galactic Centre to Galactic latitudes +/-10 bring in much of the Galactic
Bulge. This ESO public survey, begun on 28th December 2011, reaches down to
20th magnitude (10-sigma) and will provide single-epoch digital optical
photometry for around 300 million stars. The observing strategy and data
pipelining is described, and an appraisal of the segmented narrowband Halpha
filter in use is presented. Using model atmospheres and library spectra, we
compute main-sequence (u - g), (g - r), (r - i) and (r - Halpha) stellar
colours in the Vega system. We report on a preliminary validation of the
photometry using test data obtained from two pointings overlapping the Sloan
Digital Sky Survey. An example of the (u - g, g - r) and (r - Halpha, r - i)
diagrams for a full VPHAS+ survey field is given. Attention is drawn to the
opportunities for studies of compact nebulae and nebular morphologies that
arise from the image quality being achieved. The value of the u band as the
means to identify planetary-nebula central stars is demonstrated by the
discovery of the central star of NGC 2899 in survey data. Thanks to its
excellent imaging performance, the VST/OmegaCam combination used by this survey
is a perfect vehicle for automated searches for reddened early-type stars, and
will allow the discovery and analysis of compact binaries, white dwarfs and
transient sources.
