The location of the Super Bowl is determined by the NFL about 4 years in advance.
Every city can place a bid to host a Super Bowl and this bid evaluates by the NFL according to different parameters such as stadium quality(State of the art and over 70,000 seats), the capacity for guest accommodations (I heard on TV that should be at least 25k hotel rooms in one hour distance), restaurants, parking, and stadium and general city security.
I also heard that the minimal average temperature should be around 10 Celsius/50 Fahrenheit at the game date.
The NFL owners then meet and make the selection on the host city.
The Bids and the selection determine several years in advance in order the chosen city will be able to complete any construction necessary to this big event.
New Orleans, the site of the 2013 Super Bowl, invested more than $1
billion in infrastructure improvements in the years leading up to the
game.
You can also read about he history of Proposed Super Bowl Sites.
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