Pointfile
From modwiki
A pointfile is a special file generated during map compilation when there is a leak. This file is created in the same directory and with the same filename as the .MAP file but with the .LIN extension instead.
To use a pointfile, load DoomEdit and go to File > Pointfile and the editor will draw a red line. You can then use shift + ctrl + k and shift + ctrl + l to move back and forth along the line to find the leak.

