Major City vs. Giant Suburb

[Oswald Acted Alone, You Kook]

It's simple, what's the line between them?

There are a lot of very big suburbs, and a lot of major cities. Sometimes they are right next to each other, which also blurs the line. Is Ft. Worth a giant suburb of Dallas, or a major city in its own right? There's also Baltimore and DC, and of course Minneapolis and St. Paul.
 
Looking at America's largest cities, which is the last Major City (besides the capitol cities) and which is the first Giant Suburb?

[Oswald Acted Alone, You Kook]

I think the last major city was Las Vegas and the first giant suburb was Brooklyn, which was a separate city for a while.

Brooklyn isn't a suburb, it's a part of NYC.

What about Long Beach? I read somewhere that it's the largest suburb.

[Oswald Acted Alone, You Kook]

So what about Long Beach? Is it the largest suburb? (Not counting St. Paul and Ft. Worth obviously)