Thanks David, yes that is kind of helpful.
It’s still a pity they haven’t done one Mercator projection (or similar) map for the whole planet. I have now worked out that their global mosics go from 180 deg to 180 deg longitude, not from zero to zero, which was confusing me for some time. It’s still a lot of work to relate these images together, as Mercury’s suface, like that of the Moon, looks completely different under different illumibation angles. Also they’ve made a problem by reproducing all these image really dark. You have to import them ito Photoshop and turn up the levels to see much.
One of the things I’ve been trying to establish in my reasearch is if there is any valid relationship at all between telescopic maps and drawings and what is really there. Peter Grego in his 2008 Springer book on Mercury and Venus still holds that the traditional maps do represent things that can be seen repeatably by good observers. Patrick Moore, on the other hand, after Mariner 10 visited, always said that the visual maps had been ‘hopelssly wrong’. My examination of the Messenger data tends to side with him – there’s no relationship whatsoever.