Hi Trevor, Chimera doesn't move a crystallography unit cell map around to cover the PDB model you are looking at, as does O and Coot. Basically Chimera map capabilities were created primarily for electron microscopy maps that are not periodic. Still I agree that is useful for many people and we should add that to Chimera and I'll put it on our requested feature list. http://www.cgl.ucsf.edu/chimera/plans.html There are harder ways currently in Chimera to get the PDB model and map to coincide in cases where they don't when they are first opened. One is to shift the map by hand. Use the volume dialog Coordinates panel and add an integral number of unit cell shifts to the x, y, or z axes. You'd have to look at the CRYST1 record in the PDB file to know the unit cell size, or show the Unit Cell dialog (menu Tools / Higher-Order Structure / Unit Cell). If the cell angles are not 90,90,90 then it is trickier to figure out the xyz translations. Coot and maybe O too also will "wrap" the periodic map if the PDB crosses the map unit cell box into the next unit cell. In Chimera two copies of the map could be made (volume dialog menu file / duplicate), one translated by a unit cell size, and turning off "cap box faces" in the volume dialog surface and mesh options. Actually I see this does not work since Chimera knows that the two maps are the same and applies the same translation to both. That needs fixing. Even if it worked it is a lot of trouble. Again Chimera should do the wrapping. Since most Chimera map users look at electron microscopy it will need to be an optional behavior when added to Chimera. I will add this too the requested features page. Tom