How the map is made
The world is generated in your browser by a port of Valheim's own world generator (the game's WorldGenerator, its biome sectors and ZoneSystem's location placement), with the location list of version 1.0.17 read from the game files: 200 kinds of location, from boss altars to shipwrecks. Each kind is placed the way the game does it, with the same random numbers, so the spots are the game's, not guesses.
Checked against a world Valheim generated on our PC (seed v6tBhYJErE): the biomes of all 4,194,304 cells of its minimap matched, its heights matched in 99.995% of them to the game's rounding, and all 12,372 of the 12,372 locations in its save came out at the same coordinates.
Not decided by the seed: which of a trader's possible camps becomes the real one, and which way a building faces (the game rolls that when the area first loads). Ore, trees and berries are not on the map yet. What each location holds is on its own page: see locations & dungeons, bosses and traders.
Questions
›Where do I find my world's seed?
In the game's world list, under the world's name (Start game → pick the world). Or drop the world's .fwl or .fwl2 file on the map: the seed is read in your browser, nothing is uploaded.
›Will the map match my world?
It runs the world generator of Valheim 1.0.17: terrain, biomes and where each location goes. Checked against a world the game made, all 12,372 saved locations came out at the same coordinates. Worlds made before the Mistlands update used an older generator, so their terrain differs.
›Why are there several spots for Haldor, Hildir and the Bog Witch?
The generator lays out several possible camps for each (Haldor 10, Hildir 10, Bog Witch 10). The first one a player comes near is where the camp appears, and the game removes the others. The same goes for the Forge of Potential.
›How do I get to a location quickly?
Click a marker and copy its goto command. In the game, press F5, enter devcommands, then paste the command: it moves you to that spot.