If Fallout 3 is a game about spaces, then Fallout: New Vegas is a game about people.
This can be seen in the way that it informs the world design of both games. The Capital Wasteland of Fallout 3 is a vast, sprawling space with huge distances in between points of interest. The game wants the player to forge a relationship to the Capital Wasteland itself as they navigates its reaches. The Mojave Wasteland of New Vegas, on the other hand, is a lot smaller. There are several points of civilization in the wastes that are (almost) all connected by a singular road that loops around the map. In fact, this is how the game structures the first act of its main questline: you start in Goodsprings, head south to Primm, then the NCR outpost, then loop round and up to Novac, and finally New Vegas itself, all following the I-15/I-95. The distances between these pit-stops is shorter than the distance between any two locations in Fallout 3, especially without any train tunnel mazes to meander through, and there’s not much scenery in these interludes. It’s all wide, indistinct expanses of desert and the occasional valley. The Capital Wasteland always has the Washington Monument visible in the distance, drawing the player continually back to that frame of reference and forging a relationship between player and space. Not so in the Mojave.
What this does mean is that greater emphasis is put on the interactions that the player has with those pockets of civilization when they do reach them. The player is encouraged to stick around for a while and seek out all the Stuff that the developers have packed in. This is achieved through the quest design itself, which makes connections between settlements for the player to tap into. There are lots of side quests in New Vegas that simply entail bouncing between settlements to talk to different people.
Ranger Ghost in the NCR Mojave Outpost asks the player to go to Nipton to check out smoke coming from the town. When they get there, they find it has been sacked by the Legion, and Vulpes Inculta gives the player a separate quest to spread word of the Legion’s actions to strike fear into the NCR. Back at the Mojave Outpost, the player tells Ranger Ghost about Nipton, and in return get some dialogue explaining the significance of this event in terms of the conflict between the NCR and the Legion. They can also talk to Sergeant Kilborn in the Outpost to complete the quest given by Inculta.
These are quests that overlap, establish relationships between individuals, factions and locations, and also involve only travelling, observation and conversation in terms of gameplay. Rather than emphasising the movement of the player through the space of the Mojave itself, these quests ground the player in the geopolitics of the Mojave that they then become a part of. There are shades of this in Fallout 3, especially in the Broken Steel DLC, but they aren’t as well realised, nor are they as integral to the way that the game is structured as a whole.