Elaine & Tom - Thanks so much for your help. The vop cover command worked perfectly, which is a bit embarrassing because I know you've posted on that before. I thought there was a rotation involved, which I guess reflects rather badly on my ability to compare electron density maps to models. I was also thinking that it was a more complicated transformation, because I could see that the Coot map headers include some symmetry operators that were different from the working Phenix maps. (symop=x,y,z versus symop= ). ChimeraX opens the map but returns this error: Unable to parse symmetry operators of coot-map.ccp4 b'x, y, z Either way, vop cover solves the problem. gsb ………………………………... Gabriel Brandt Assistant Professor Department of Chemistry Franklin & Marshall College PO Box 3003 Lancaster, PA 17604 ph: 717.358.4846 shipping address: 415 Harrisburg Ave Lancaster, PA 17603 ………………………………...