The Quick Map commands present an alternative to the Map commands. Quick maps are read directly from the map file and are handled in core. The map formats currently recognized are CCP4, X-PLOR, TNT, PHASES and EZD. The crystallographic symmetry operators are used to expand the map on the fly, so it is only necessary to calculate the electron density in an asymmetric unit. The program associates a short name with each map, by default Q1, Q2, etc. All operations on the map must be referenced with this short name. There is currently a limit of 5 maps.
The Quick Maps are quicker than the old style maps because the contoured density is stored in the computer. If you go back to an area that you have already contoured, the program will not repeat the calculations, only redisplay the contours that were already calculated. However, contours are not stored indefinately; if O runs out of graphics memory, it employs a caching algorithm, deleting the oldest bits of density first.
The advantage of the Quick Map system is most apparent if you are working with fitting, only displaying small boxes of density at any time. If you need to display large cubes of density, you should use the Map or EZD options.