Hi Atsutoshi, You should be able to open the XPLOR format file using Chimera menu entry File / Open.... If the file name ends in ".xplor" it will be opened in XPLOR format. Or if it has a different file suffix you can choose "all (ask type)" from the File / Open dialog "File type" menu, then open the file and you will be asked to identify the file type from a list. Choose "CNS or XPLOR density map". Opening the file will display it as a contour surface using the volume viewer tool. You may want to switch to "solid" display style in the volume dialog. By moving the square nodes on the data histogram in the volume dialog you can adjust brightness and control what map values are displayed. Chimera can also directly compute occupancy of water or ions from an MD trajectory. See the "occupancy analysis" section of the Chimera MD Movie tool documentation: http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/movie/framemovie.ht... Tom