Map files are stored in directory id_low = 0xd710, id_high = 0x9305 in the Master file table. They contain the gameplay relevant details of a map. This includes heights, collision data, event triggers, and so on. They do *not* include graphics (tile sets, tile maps, palettes, etc.), those are stored elsewhere (TODO: Where?).

Most (all?) maps are stored LZ77 (swi 0x11) compressed. When loading a map, the game checks if the map file starts with the ASCII characters "HP" (hex: 0x48, 0x50). If it does, then the map file is not compressed, and used by the game as-is. If it does not start with these characters, the game will LZ77 decompress it to EWRAM (in Boktai 1: to 0x0202a400).

File format

Type	Description
char[4]	Magic number ("HP\0\0")
u32	Offset from start of file to #Tile data
u32	Offset from start of file to #Zones
u32	Offset from start of file to unknown block 1 (maybe related to enemy patrolling?)
u32	Offset from start of file to unknown block 2 (maybe related to enemy patrolling?)
	Tile data
	Zones
	Unknown block 1
	Unknown block 2

Tile data

struct tile_data {
  u32 unknown_1;
  u16 width;
  u16 height;
  u32 unknown_2;
  tile[height*width] tiles;
};

// Note how stairs and height are packed into a single byte, making this struct 4 bytes long.
struct tile {
  tile_effects effect;
  u8 obj;
  tile_stairs stairs : 4;
  u8 height : 4;
};

// Bitmask, multiple effects per tile are supported
enum tile_effects : u16 {
  wall = 0x0002,    // an always inaccessible tile
  unknown = 0x0004  // sometimes used directly on loading zone tiles
  noise = 0x0020,   // alerts enemies when stepping onto the tile
  ice = 0x0040,
  lava = 0x0080,
  void = 0x0100,    // fall down and die
  unknown = 0x0400, // wall-ish
  unknown = 0x0800, // sometimes used near loading zones pointing NW
  unknown = 0x1000, // sometimes used near loading zones pointing NE
  // other bits unknown
};

enum tile_stairs : u8 {
  none = 0,
  vertical = 1,   // from south -> north
  horizontal = 2, // from east -> west
};

tile.obj: This determines the sprite that is used to occlude Django when he should be covered by the tile. Purely visual. 0 = default, other values need to be documented.
tile.height: A tile is only accessible to Django if he's either coming from a tile at the same height, or coming via a suitable stair tile.