Hi Eleanor

Electron scattering factors can be negative for negative ions, particularly at low d*.  For a low-resolution map it means that the electric potential is the opposite sign to what you expected.  It's why you often don't see ASP & GLU side-chains in low resolution EM maps.

Cheers

-- Ian

On 15 March 2018 at 14:17, Eleanor Dodson <0000176a9d5ebad7-dmarc-[log in to unmask]> wrote:

I am pig-ignorant about these ,, but this example has negative values as well as positive..

What does this mean? I thought a well phased map would be pretty well all positive..

 Eleanor