have you come across this composite map? - it's low resolution, but as far as I can tell, shows the higher latitudes to some depth. regards Ray
http://astrometry.fas.harvard.edu/skymaps/halpha/
http://astrometry.fas.harvard.edu/sk...s/comp_big.jpg
EDIT: and to give an idea of the scope of surveys like VPHAS+, the zoomable image from a sister NIR survey of the centre of the milky way is jaw dropping.
http://www.gigapan.com/gigapans/117375. I guess that this also shows another reason for restricting the length of exposures - the brighter star PSFs cover nearby regions - in a dense star field, the skirts of the brighter stars ultimately obliterate deep data as you expose longer. As an aside, I find that this image provides a way of visualising large numbers, for example, every star in this image could correspond to 80 people if one wanted to to get a feel for the size of earth's human population.