The title Fallout 4 hasn't been announced so it could be anywhere in the United States. But if your referring Fallout 4 to New Vegas (comon mistake) it as the title explains in Las Vegas.
Nothing in New Vegas spoils Fallout 3. They take place in 2 completely different corners of the country. And New Vegas can not spoil anything for Fallout 3, as New Vegas takes place before the events of Fallout 3. Hope this helps! Also Fallout 3 is not a sequal. But lets pray for a Fallout 4
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Fallout is the residual radiation that falls out of the atmosphere after a nuclear explosion .If you mean the video game it takes place in 2077
There are rumors of a Fallout 4 taking place in San Francisco, but as of 2/26/12 (today's date) there is no official news.
I could imagine that it takes place in America just like every single other game in the Fallout series.
There is no such place in fallout 3.
Fallout 3 takes place in the year 2277, 36 years after the setting of Fallout2
A fallout shelter is a place were people would hid there stuff
A fallout shelter is a place were people would hid there stuff
They most likely will, though Obsidian is making Fallout: New Vegas (which is not Fallout 4, it's just another game in the Fallout world)
There is no official cover system on Fallout 3, but sure you can take cover.
After new Vegas will be 5 more fallout 4 fallout arctic meltdown fallout raider version fallout pre war edition and fallout final