Tile format (from valheim-map.world export Readme.txt):

Each tile is a gzip-compressed binary file containing a flat array of:
  struct MapSample {
    uint16_t biome;     // 2 bytes - biome enum
    float height;       // 4 bytes - height in Valheim units
    float forestFactor; // 4 bytes - forest density
  }  // = 10 bytes per sample

1024 x 1024 samples per tile = 10,485,760 bytes uncompressed
4x4 tiles = 16 tiles total
World: 24000 x 24000 Valheim units

Biome enum:
  None=0, Meadows=1, Swamp=2, Mountain=4, BlackForest=8,
  Plains=16, AshLands=32, DeepNorth=64, Ocean=256, Mistlands=512

locations.json: list of every location with prefab name, position, contents
map.json: world metadata (seed, tile size, version)