UNSPLT reads file:

my_project.spt

from CWD, where my_project is a placeholder for the project name entered by the user
in response to the sole prompt from UNSPLT. 

The file my_project.spt contains

Line 1: JX - an integer indicating the number of segments in the X-variable direction
Line 2: JY - an integer indicating the number of segments in the X-variable direction

all other gridding information is read from perplex option file specified in the 
my_project.dat resident in CWD.

UNSPLT reads the segments row-wise through the loop

      do j = 1, jx
         do i = 1, jy
c                                 segment index
            k = k + 1

         end do 
      end do 

where for each value of the segment index k=####, the data is read from 

./my_project/segment####/files

the segments share edges.