Explorer

Explorer is a Fallout, Fallout 2, Fallout 3 and Fallout Tactics Perk.

Fallout, Fallout 2 and Fallout Tactics
The mark of the Explorer is to search out new and interesting locations. With this Perk, you have a greater chance of finding special places and people in random encounters.

Fallout 3
When you choose the Explorer perk, every location in the world is revealed on your map.

It should be noted that this doesn't allow you to fast travel to any of the locations it reveals, and doesn't add them to your Geomapper Module for the Geomapping with Reilly quest.