Re: Request for technical information
It looks like a detailed picture, but when you consier the actual size of the moon, you'll see that this particular map isn't actually that high resolution.
The technique that GRAIL uses is derived from a similar system called GRACE that mapped the Earth... bit more data available on the relevant wiki page, etc, and a bit of searching the interwebs may provide you with similar information from more trustworthy sources. The technique is very neat, though not trival to explain, but basically it involves two spacecraft in the same orbit measuring the changes in their relatative separation over time.
GRACE managed a 200km resolution for its gravity map of Earth, but from a much higher altitude. I can't find actual numbers for GRAIL right now, but they'll likely be of the same order.