Set the data file coordinate system by opening the data file in the Surfer worksheet and using the worksheet's Data | Coordinate System | Assign Coordinate System command. The spatial reference information is saved in an external GSR2 file. Each time you use the data file (e.g. to create a grid or a post map), the coordinate system will automatically be applied. Please note that in order for the data file to be linked to the external spatial reference file, they both need to be in the same folder.
Updated September 26, 2017