Ian is, as always, absolutely right. The only comment/correction I have is that Hailang was apparently referring to severely incomplete model, for which the poor phases will dominate the mFo map. Under such circumstances, even 2fo-fc map will not correctly reflect the actual relative contribution of the missing and already modeled regions into electron density.
On Wed, 2010-09-01 at 10:49 +0100, Ian Tickle wrote: > This is not true. The 'model map' (i.e. the map calculated from the > model) is obviously the one with coefficient DFc. The mFo map > represents the model (i.e. the structure already placed) + *half* of > the missing structure (represented by mFo-DFc) -- "I'd jump in myself, if I weren't so good at whistling." Julian, King of Lemurs