Hi Karim,
You can use the command "volume zone" with "newMap false":
<http://rbvi.ucsf.edu/chimerax/docs/user/commands/volume.html#zone>

For example, if your map is #2 and your atomic model is #1 with chain of interest B, could be something like:

volume zone #2 near #1/B range 5 newMap false

(or "near sel" to use currently selected atoms instead of "near #1/B" to specify the chain directly).  Then to go back to the full map display, command:

volume unzone #2

<http://rbvi.ucsf.edu/chimerax/docs/user/commands/volume.html#unzone>

I hope this helps,
Elaine
-----
Elaine C. Meng, Ph.D.                      
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Apr 2, 2020, at 9:36 AM, Karim Rafie <karim.rafie@umu.se> wrote:
>
> Dear all,
> I was wondering how to show part of a map only surrounding certain residues, i.e. I have coordinates for a multiple-chain PDB but I only want to show the electron density surrounding one chain.
> Any help would be greatly appreciated.
> Best,
> Karim