These files are located in save game folders (master_patches\SAVEGAME\SLOTxx\, where xx is from 01 to 10). They store maps of cities and othe locations.
The names of SAV files match the names of MAP-file maps.
The internal format matches the format of MAP files, but the files are compressed using the GZIP algorithm. If you change the extenion from SAV to GZ or ZIP, they can be uncompressed with archive utilities such as WinRAR or Total Commander.
In each slot there is another file, AUTOMAP.SAV, which contains an AUTOMAP.DB file. This stores some data about the current map in the saved game, but its format and exact contents are not known.
Original document at teamx.ru (in russian)