The LNDSEA1.DAT file contains a bit map of the land/sea area of the earth. Using the file, a specified point of latitude and longitude can be determined to be land or sea. A routine, LNDSEA, opens the file and provides a flag to indicate if the specified point is land or sea.
Fortran file unit 1 should be reserved for accessing the map data file by these routines. The logical name LONGLOC: must be assigned to be the directory containing the LNDSEA1.DAT file.