Major City vs. Giant Suburb

[pbrower2a]

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?

Fort Worth is a large city in its own right.

1880    6,663       —
1890    23,076       246.3%
1900    26,668       15.6%
1910    73,312       174.9%
1920    106,482       45.2%
1930    163,447       53.5%
1940    177,662       8.7%
1950    278,778       56.9%
1960    356,268       27.8%
1970    393,476       10.4%
1980    385,164       −2.1%
1990    447,619       16.2%
2000    534,697       19.5%
2010    741,206       38.6%
Est. 2013    792,727       7.0%

1850    1,073       —
1860    698       −34.9%
1870    3,000       329.8%
1880    10,358       245.3%
1890    38,069       267.5%
1900    42,639       12.0%
1910    92,104       116.0%
1920    158,976       72.6%
1930    269,475       69.5%
1940    294,734       9.4%
1950    434,469       47.4%
1960    679,684       56.4%
1970    844,401       24.2%
1980    904,078       7.1%
1990    1,006,977       11.4%
2000    1,188,580       18.0%
2010    1,197,816       0.8%
Est. 2013    1,257,676       5.0%

It has never been bigger than Dallas, but it has its own suburbs -- and shares some with Dallas. Minneapolis and Saint Paul, Tampa and St. Petersburg, San Francisco and San Jose, and Baltimore and Washington do that, too.

A city between them (Arlington) is one of the largest suburbs in the United States.