Minecraft wiki entry for Explorer_Map, associated text: When a cartographer generates the trade offers for the explorer maps, it chooses the location of one of the nearest structures of the respective type (monument or woodland mansion).
For the reason above, explorer maps obtained from one cartographer are always the same. Also, if two cartographers unlock the explorer map trades approximately at the same place and at the same time, the map locations are usually identical. This sometimes also happens when finding multiple treasure maps from ocean ruins.
Explorer maps fill as the chunks are generated, rather than when the player holds them while in the area; leaving an explorer map while exploring the area still fills the map.
Buried treasure explorer maps are named Buried Treasure Map in Java Edition while in Bedrock Edition, they are named Treasure Map.
It is possible for a cartographer to give a monument or woodland mansion explorer map for areas where the structures would have spawned in the world, but were unable to as a result of terrain generation. As a result, explorer maps, unfortunately, don't always guarantee that a structure exists at the purported location. This is most common with woodland mansion explorer maps, due to its generation algorithm.
On Bedrock Edition, inventory editors and add-ons can be used to create Explorer Maps that lead to any structure.