This text file contains a list of all maplets that could possibly overlap a new map created in the same location used to make a bigmap.
If it's present, programs use LMRKLISTO.TXT to calculate overlaps, rather than using LMRKLIST.TXT. This enables lithos and lithosP to run faster because they only search for overlaps among a limited set of landmarks.
When bigmap runs, it keeps track of all the maplets that went into its construction and puts this list into USED_MAPS.TXT. If you want to use this reduced set of landmarks, you can get it from USED_MAPS.TXT after you run bigmap. Once it is complete, LMRKLISTO.TXT contains all the maplets that could possibly overlap a new map created in the same location used to make the bigmap. Moreover, as LITHOS creates new maplets, it automatically adds them to LMRKLISTO.TXT.
cp USED_MAPS.TXT LMRKLISTO.TXT
(Compiled by JRW and EEP)