The default when digitizing and saving the data from the Digitized Coordinates window to a BLN file is to Assign NoData (blank) inside the boundary (a BLN flag of 1). If you wish to Assign NoData (blank) outside the boundary when you save the BLN file, click Options | No Data Inside Region in the Digitized Coordinates dialog to uncheck that option. Then click File | Save and save the BLN file. The BLN flag value will be 0.
In Surfer 12 and previous versions, the blanking flag is always set to 1 when saving a BLN file from digitizing. You change the flag value manually after the BLN file is saved by clicking File | Open and opening the BLN file in the worksheet, set the blanking flag value of cell B1 to 0, and save the changes.
Updated October 18, 2018