In IDL Object Graphics the routines that one uses to map map coordinates to cartesian coodinates and vice versa are MAP_PROJ_INIT, MAP_PROJ_FORWARD and MAP_PROJ_INVERSE. 'MAP_PROJ_INIT' does work similar to 'MAP_SET' in setting up IDL's '!MAP' structure that defines the mathematics of the projection you have chosen. (You can also continue to use MAP_SET for this, but I think MAP_PROJ_INIT has enhanced functionality.) MAP_PROJ_FORWARD and MAP_PROJ_INVERSE use the state of the current !MAP struct to calculate the mapping of the points you give as argument. You might also be interested in MAP_PROJ_IMAGE, which can warp your images defined by an evenly gridded spatial coordinates to your the projection currently stored in !MAP. Regards, James Jones