The other answers are correct that New Orleans is on a river delta close to the ocean and Las Veas is in the desert (a long way from the ocean).

Las Vegas was a small town until the middle of the 20th century – when it became a home for gambling casinos.

New Orleans was built in the 1700s to be the premier port on the Mississippi River for goods being transported from North America’s interior to Europe.

However, the other answers are NOT correct about New Orleans being "below sea level". Most of New Orleans is above sea level and the parts that are below are usually only a bit below. It is a consequence of building a city on a river delta.

http://en.wikipedia.org/wiki/New_Orleans

http://en.wikipedia.org/wiki/Las_Vegas%2C_Nevada
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New Orleans resident

http://www.neworleansonline.com/neworleans/history/people.html

http://www.kunstler.com/excerpt_lasvegas.htm
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New Orleans, LA: It’s swampy, humid and muggy during the summer. It’s chilly one day, and in the 70’s or 80’s the next… in the winter, weather changes a lot. New Orleans, in terms of fun, has lots of strip bars, crazy people and bars, bars, bars. Don’t forget Mardi Gras; nobody does Mardi Gras like the Orleanians.

Las Vegas, NV: During the summer, it’s temperatures reach extreme highs, but it’s dry heat, no humidity at all. It’s in the desert, while New Orleans is almost or becoming completely submerged in water. It’s in a somewhat high altitude area, and New Orleans is 6ft. below sea level. For fun, Vegas can bring you tons and tons and tons of casinos, crazy people and a whole lot more.

I like Las Vegas’s version of fun better, but I like New Orleans’s weather conditions more.

:] hope that helped.
by the way, I haven’t been to Las Vegas in the winter, so I couldn’t tell you about that.
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