LOC.DAT has a row width of 20 bytes. There are a total of 50 records (not all of them necessarily used) for a fixed file size of 1,000 bytes. Most of this info is from NKF (thanks a lot) and some was ripped from Hatfarm / Chris Voss's great pages.
00 - Unused Entry 01 - Alien Ship (moving or crashed) [CE: moving or landed] 02 - X-COM Ship 03 - X-COM Base 04 - Alien Base 05 - Crash Site 06 - Landed UFO unused 07 - Waypoint 08 - Terror Site unused in TFTD, see below: Extras for TFTD only: 0x51 - Port Attack 0x52 - Island Attack 0x53 - Passenger/Cargo Ship 0x54 - Artefact Site
|1||0x01||Object table reference - Possible values - 00 to FF - Just a reference. This just shows how many there are of this type on the geoscape. If the object is either a UFO (Alien Ship for TFTD) or X-COM craft, then this is the index into CRAFT.DAT. If the object is an X-Com base, then this is the index into BASE.DAT and if it is an Alien Base this byte contains the race:
UFO TFTD 0 = Sectoid Aquatoid 1 = Snakeman Gillman 2 = Ethereal Lobsterman 3 = Muton Tasoth 4 = Floater Mixed Crew (Type I) 5 = Final mission mix Mixed Crew (Type II)
|2-3||0x02-0x03||Horizontal coordinates or longitude (low bit then high bit respectively). 0 - 2880|
|4-5||0x04-0x05||Vertical coordinates or latitude (low bit then high bit respectively). -720 - 720|
|6-7||0x06-0x07||For crash site or terror site - countdown timer (in hours). For moving objects - how many game ticks (5s) have to pass until craft moved to next globe coordinate (cell_size div speed).
|8-9||0x08-0x09||Fractional part of how much is left to the next globe coordinate (cell_size mod speed), used only for moving objects.|
|10-11||0x0A-0x0B||Count suffix of the item, eg: Skyranger-1 or Crash Site-47. It appears to have no meaning for XCOM Bases, but for other types where it is set, 0B is the high byte for when you go over 255 UFO's or crafts, etc.|
|14||0x0E||Craft transfer mode:
0 = Not transferred 1 = In transfer 2 = Selected to transfer (temporary value)
|16-19||0x10-0x13||Globe object visiblity/mobility bitfield:
0 (value 1) Hidden object flag (unrevealed alien bases, xcom crafts at base, undetected UFOs) 1 (value 2) Moving object flag (UFOs, flying XCOM crafts except for when patrolling). 2 (value 4) Targeted UFO flag (set to 1 when alien craft targeted). Used for UFO decode menu popup when UFO craft reappears.