How do the names for the maps in Minecraft work?

The first map created is map_0, the second created is map_1, the third created is map_2, and so on, up to map_65535. Note that each time you zoom out "one" map, it actually creates a new map with a new map name.

Aside, you can give your maps more memorable names by renaming them in the anvil.

When you craft a map, it will be named Map_0 . if you make another map in the same area, it will also be named Map_0 . if you go out of Map_0's boundaries, you can create a new map and it will be called Map_1 . You can keep repeating the process over and over up until Map_65535 . each map in your inventory retains its FOW (Fog of war) covering, even if the maps are the same name. It will also retain FOW when dropping the map and exchanging them.

Hope this answered your question!

Sources: @SevenSidedDie (map numbering), Firsthand experience in Minecraft 1.7.3 (both SSP and SMP), Yogscast (Observing map properties in adventure map videos and Update videos)

The map names just help you remember which map is which. The seed is what makes each level different.