Wasteland is not empty. And altough it's looking nearly dead its certainly isn't. Every day Ants dig holes, Radscorpions lurks for preys, Geckos wander in pointless circles and Deathclawes decorate their nests with human skulls...what? Nevermind.
To represent this in game world sometimes on map you can find a red dot marking a random event location. They are various and well random. They tend do dissapear pretty quick so be sure to hurry.
Note: Encounters are visible for many people at once. Its really possible that when you enter such location other player will be allready inside or vice versa. If players killers catch you while fighting NPC's inside you might be in tough spot.