MAPS.BSA

Overall, the Maps.BSA file contains 61 total regions with a combined total of 15251 locations, with 4232 of these being dungeon types.

Contents

General File Layout

The file starts with a short BSA header followed by the map data as sorted by map region (the provinces such as Wayrest, Glenpoint, Daggerfall etc... in the game). Each region is furthur divided into other data sections. Each data section is referenced by a directory entry which occurs at the end of the file as per a usual BSA file.

	BSA Header
	Begin Region
	  Location Offset Section 	} MapPItem
	  Location Record Data		} MapPItem
	  Dungeon Offset Section	} MapDItem
	  Dungeon Record Data		} MapDItem
	  Table Data			} MapTable
	  Name Data			} MapNames
	End Region
	...Other Regions...
	Map Directory

MapPItem

Location Offset Section

Offset sections appear before each section of town record data. It is merely a list of 4 byte long values which point to the start of a location record relative to the end of the offset section.

Location Record Data

Each record is pointed to by one offset record in the preceding offset section. Records are variable length. Contains all locations of the region (town, dungeon, house, etc...). 
	[Bytes 0-3]	long PreRecordCount
		Gives the number of 6 byte records which follow.  This value
		can be 0x00000000 indicating that no records exist.  The
		record data has no visible effect on the location. Values 
		here range from 0 to 555 (confirmed) (around 20% of location
		and dungeon records have no prerecords).  Total of 569407
		prerecords in the MAPS.BSA file.
	[Bytes 4...]	unsigned char PreRecords[6]
		The 6 byte record data if there is any.
	[Bytes ...]	Header Information, 0x47 (71) bytes			
		[Bytes 0-3]   	long  OneValue1 = 0x00000001;
			Always this value in both location and dungeon records
			(confirmed).

		[Bytes 4-5]   	short NullValue1;
		[Byte  6]     	char  NullValue2;
			Always 0 (confirmed).		
		[Bytes 7-10]  	long  XPosition;
			Position of the location in game position units.
			Values can range from 51,200 (far West) to around 
			32,389,120 (far	East) (confirmed).
		[Bytes 11-14] 	long  NullValue3;
			Always 0 (confirmed).
		[Bytes 15-18] 	long  YPosition;
			Position of the location in game position units.
			Values can range from around 40,961 (far South) to
			16,332,801 (far North) (confirmed).
		[Bytes 19-22] 	long  Unknown1;
			Location records always have 0x00008000 (32768).
			In dungeon records this value is always 0 (confirmed).
		[Bytes 23-26] 	long  Unknown2;
			Values range from 0 to 18 in location records (is 0 
			~75% of the time).  In dungeon records this value is
			always non-zero in the range 65536 to 589824
			(confirmed).
		[Bytes 27-30] 	long  Unknown3;
			Almost always non-zero in all records.  Location record
			values range from 0 to 1832, dungeon values range from
			0 to 684 (confirmed).
		[Byte  31-32] 	short OneValue2 = 0x0001;
			Always 1 in both dungeon/location records (confirmed).
		[Bytes 33-34] 	short LocationID;
			The unique location ID which is used for quests and
			probably other things.
		[Bytes 35-38]	long NullValue4;
			Always 0 in both dungeon/location records (confirmed).
		[Bytes 39-40]	short Unknown4;
			Always 0 in location records and always 1 in dungeon
			records (confirmed).
		[Bytes 41-44]	long Unknown5;
			Always 0 in location records and takes a variety of
			values in dungeon records (always non-zero) (confirmed).
			These last two might indicate the presence and size
			(or offset to) dungeon specific data.
		[Bytes 45-70] 	char NullValue5[26];
			Always 0 in both dungeon/location records (confirmed).
	[Bytes ...] char LocationName[32]
		Gives the location name.  Data is always 32 bytes in size and
		string should be NULL terminated. Any extra data after the 
		string is ignored. The name is used when you enter the location
		but not used when on the travel map (the Name Table is used for
		that).
	[Bytes ...] char Unknowns[9];
		Unknown values
	[Bytes ...] short PostRecordCount
		Gives the number of records which follow.  Records appear
		to be of fixed length 0x1A (26) bytes.  Always 0x0000 in dungeon
		records.
From this point on the dungeon/location records differ slightly.

Location Records

	[Bytes ...] char Unknowns1[5];
		Unknown values.
	[Bytes ...] char LocationPostRecords[26][]
		See the Location PostRecords Format section below.  Each record is
		0x1A (26) bytes in size. 
	[Bytes ...] char AnotherName[32];
		Appears to be another name for the location but its purpose is 
		unknown.  Changing it has no visible effect.
	[Bytes ...] long Unknown6;
		This value is the same as the first 4 bytes in the MapTable for
		the location.  Another location ID perhaps.
	[Bytes ...] char Unknowns2[4];
	[Bytes ...] byte BlockWidth;
	[Bytes ...] byte BlockHeight;
		Range from 1 to 8 and give the size of the location in blocks. The
		BlockWidth*BlockHeight will give the number of block file numbers
		in the following sections.
	[Bytes ...] char Unknowns3[7];
	[Bytes ...] char BlockFileIndex[64];
		Each can be an index, from 0 to 44, of a block file.  See
		Appendix C for more information.  Usually just the first index
		is used and the rest are zero.
	[Bytes ...] char BlockFileNumber[64];
		Similarily gives the block file number, from 0 to 42.
	[Bytes ...] char BlockFileChar[64];
		Similarily gives the block file character, from 0 to 143.  See
		Appendix C for possible values.
	[Bytes ...] char Unknowns4[32];
		Typically zero but almost all values range from 0 to 122.
	[Byte  ...] char Unknown5;
		Ranges from 0 to 18, usually 0.
	[Byte  ...] char Unknown6;
		Ranges from 0 to 22, usually 0.
	[Bytes ...] char NullValues1[9];
		Always 0 (confirmed).
	[Bytes ...] long Unknowns7[22];
	[Bytes ...] char NullValues2[40];
		Always 0 (confirmed).
	[Bytes ...] long Unknown8;

Dungeon Records

	[Bytes ...] long Unknown6; 
	[Bytes ...] long Unknown7; 
	[Bytes ...] short NumDungeonPostRecords;	
		Gives the number of dungeon post records.
	[Bytes ...] char Unknown8[5]
	[Bytes ...] char DungeonPostRecords[][4];
		Each is 4 bytes in size.
	[Bytes ...] char Padding[];
		Variable size of data which appears to always be zero and may 
		simply be padding for the dungeon post records. The padding
		size is equal to  (128 - NumDungeonPostRecords*4).

2) Location Types

In Appendix B, the location types are listed. 0xAC (172) is listed as Dark Pink, 
but it looks red to me. In fact, the difference between  0xAC and 0x8C is a mystery.

Looking at the locations corresponding to each of these, I have come up with names for them:

0x84 (132) = Major Dungeon
0x87 (135) = Fortress (Large Dungeon)
0x8A (138) = Ruins (Small Dungeon)
0x8C (140) = Graveyard
0x8D (141) = Coven

0xA0 (160) = Large Town
0xA1 (161) = Medium Town
0xA2 (162) = Small Town
0xA3 (163) = Farmstead
0xA6 (166) = Tavern

0xA5 (165) = Temple
0xA9 (169) = Shrine

0xA8 (168) = Palace / Manor
0xAB (171) = Shack
0xAC (172) = Graveyard
UPDATE! From ATLAS.C: 
/*	The color code has a fine structure as well.
	When a new character is rolled, the sites tagged
	0x8n are rolled against to determine which of them
	are eligible to include on the overhead map from
	the beginning.  All other 0x8n sites are initially
	hidden on the map.  Conversely, 0xan sites are never
	obscured on the overhead map.  0xad (not shown) is the
	code assigned to the ship sites. */

Location PreRecords Sub-Format

The format for the 6 byte prerecord data found in the location and dungeon record data is as follows: 
	[Bytes   0-1]	short PostRecordIndex;
		Dungeon Records:
			0xFFFF - Always this value (confirmed)
		Location Records:
			Appears to give be postrecord index which the prerecord
			may apply to. The same index may be repeated in several 
			prerecords.
	[Byte    2]	char  NullValue;
		Always 0x00 in both dungeon/location records (confirmed).
	[Byte    3]	char Unknown3;
		Dungeon Records:
			0x00 - Only 23 records.
			0x10 - About half of records (10334).
			0x40 - About half of records (10415).
			0x80 - Only 17 records.
		Location Records:
			0x10 - About 20% of records (106905).
			0x20 - Around half of records (248908).
			0x30 - Only 100 records.
			0x40 - About 10% of records (59384).
			0x50 - Only 54 records.
			0x60 - Only 53 records.
			0x80 - Only 17 records.
			0xA0 - About 20% of records (133138).
			0xB0 - Only 51 records.
			0xE0 - Only 25 records.
	[Byte    4]	char Unknown4;
		Dungeon Records:
			Always non-zero and usually less than 0x0A but ranges
			up to 0xE7 (231).
		Location Records:
			Takes on a wide range of values 0-0xFF, usually
			non-zero (confirmed).
	[Byte    5]	char Unknown5;
		Dungeon Records:
			0x00 - Only in 32 records
			0x01 - Only in 8 records
			0xFA - Occurs in most records (20749)
		Location Records:
			Usually always less than 0x09 but 166572 records have
			the value 0xFA.
The arrangement of variables above is arbitrary as the actual purpose of data is currently unknown. PreRecords usually appear in location records. Only 20789 (3.7%) of the 569407 total prerecords in MAPS.BSA occur in dungeon records. The number of prerecords is generally smaller in dungeon records than location records as well. Prerecord numbers range from 0 to 27 in dungeon records while 0 to 555 in location records. The data has no visible effect on the location. The data can be mangled or simply removed with no apparent effect on the location.

Location PostRecords Sub-Format

Records which appear after the location name in the location record are 0x1A (26) bytes in size and have the format listed below. Location postrecords only occur in location records, not dungeon which have their own post record format. The number of prerecords in location records range from 0 to 329 with a total of 328499 in the MAPS.BSA. There are usually no postrecord information (97%). 
	[Bytes 0-1] 	short HouseNameType;
		Affect the generation of the house name.  Ranges from 0 to
		0x81DD (33245).
			00 00 = The Dancing Chasm (Tavern)
			01 00 = The Knave and Scorpion (Tavern)
			02 00 = The Dancing Chasm (Tavern)
			00 09 = The Silver Scorpion (Tavern)
			BA 29 = The Golden Stag (Tavern)
			BB 29 = People of Alik'r (Temple)
			EA 7E = The Queen's Dungeon (Tavern)
	[Bytes  2-17] 	char NullValues[16];
		Always 0 (confirmed).
	[Bytes 18-19]	short Faction;
		Faction number from faction.txt. Usually zero and ranges from 
		0 to 852.
	[Bytes 20-21]	short Sector;
		This value seems to generally increase with each postrecord.
		Changing this number at all crashes the game when the location
		is loaded. Always non-zero and ranges from 4 to 2329.
	[Bytes 22-23]	short LocationID;
		This value is always the same as the location ID in the the 
		location record header (confirmed).
	[Byte 24] 	char HouseType;
		Something to do with the house name or type, ranges from
		0 to 0x18 (24).
			0x00 = Alchemist
			0x01 = For Sale
			0x02 = Armorer
			0x03 = Bank
			0x04 = Town4
			0x05 = Book store
			0x06 = Clothing shop
			0x07 = Furniture shop
			0x08 = Jeweler
			0x09 = General store
			0x0A = Library
			0x0B = Guild hall
			0x0C = Pawn shop
			0x0D = Weapon shop
			0x0E = Temple
			0x0F = Tavern
			0x10 = Palace
			0x11 = House1
			0x12 = House2
			0x13 = House3
			0x14 = House4
			0x15 = House5
			0x16 = House6
			0x17 = Town23
	[Byte 25] 	char HouseQuality;
		Always non-zero and ranges from 1 to 0x14 (20).
		Divide this by 4 to get the rating on the rusty-
		relics..incense scale.

Dungeon PostRecords Sub-Format

  The Dungeon PostRecords are each four bytes long and have the following 
  format:

	[Byte 0] signed char x
	[Byte 1] signed char y
	[Byte 2] unsigned char blockNumber (low byte)
	[Byte 3] 
	    [bits 0-1] (high bits of blockNumber)
	    [bit 2] Set to 1 if the player starts in this block, 0 otherwise
	    [bits 3-7] unsigned char blockType

The blockType is actually an index into a character array at offset 001B:3E44 of Fall.exe:

const char blockTypes[6] = {'N', 'W', 'L', 'S', 'B', 'M'};

When the appropriate character is concatenated to the seven-digit decimal representation of the blockNumber, the name of an RDB file is constructed. (For example, "N0000019.RDB")

The x and y values place the block on a 2D grid. Generally, the central block of the dungeon is at (0,0).

Note: the only file that requires the two extra bits of blockNumber is S0000999.RDB. This file is only used in Privateer's Hold.

Also note: there are no RDB files that begin with "L" and there are no Dungeon Post-Records that refer to L.

MapDItem

Dungeon Offset Section

Dungeon Offset sections appear before each section of dungeon record data and follow immediately after the end of the town record data for a region. 
	[Bytes 0-3] long DungeonCount
		The number of dungeon records which follow.
	[....] Offset Section Records
		Records are 8 bytes in length and have the following structure:
			long Offset   = Offset to record data from end of the
					offset section
			short Number  = 0x0100 usually?
			short Unknown = Another increasing number

Dungeon Record Data

Each record is pointed to by one dungeon offset record in the preceding dungeon offset section for the region. Records are variable length. Only locations that are dungeons, ie, that have new interior maps, are included here. Assumably this section defines the map 'blocks' which make up the dungeon. For now this appears to be the same as the Location Record Data.

Location Table Section (MapTable)

Contains data related to to the locations in the previous sections for the current region. Starts immediately after the last dungeon record data. The number of section records is the number of the towns in the current region. Each record is 17 bytes in size and appears to be a bit field (bit fields are identified by the 6.# where # here would represent the #th bit in the 6th byte, the 8th bit would be the 0th bit in the next byte). 
	[Byts 0-3]    long Unknown1; (32 bits)
		This number is repeated in the location record.  Perhaps a 
		unique identifier of some sort.
	[Bytes 1-4]   char Unknown2; (8 bits)
		Possibly always 0.
	[Bytes 5-6.1]   unsigned int XPosition; (17 bits)
		Gives the X-position of the location for display on the travel
		map.  One pixel appears to equal 128 units with the origin
		at the bottom-left of the map.  Values should range from
		0 (far left) to 128000 (far right) (unconfirmed). Each unit
		is equal to about 256 position units in the game.
	[Bytes 6.2-8]   int LocationType; (15 bits)
		Type of the location (home, dungeon, town, etc...).  This
		determines the color of the location on the travel map.
	[Bytes 9-10]  unsigned short YPosition; (16 bits)
		Gives the Y-position of the location for display on the travel
		map. Ranges from 0 (map bottom) to 64000 (map top) (unconfirmed).
	[Bytes 11-12] short Value2; (16 bits)
	[Bytes 13-16] long Value3; (32 bits)

Location Name Section (MapNames)

Repeats all the town names in the current region. Each town name is 32 bytes, NULL terminated, and starts immediately following the town name header section. The town name offset section for the next region starts immediately after this town name data. This is the name used on the travel map. 
	[Bytes 0-3]  long LocationCount;
		Number of locations in list.  This value might be used to
		determine the total number of locations in a region.
	[Bytes 4...] char Names[32][...];
		All the location names (max 32 characters including NULL
		terminator).

Map Directory

The map directory is the last 4464 bytes of the Maps.BSA file and is the usual 0x0100 BSA directory type. It contains 248 records of 18 bytes each (for 62 regions, 000 to 061). The filenames are of the form
MAPPITEM.0##
Place item offset data and records
MAPDITEM.0##
Dungeon offset data and records
MAPTABLE.0##
Map table
MAPNAMES.0##
Name table
where ## ranges from 00 to 61 (for each region). Assumably the DF engine requests the data by this filename. See Appendix A for a list of which regions correspond to which values.