To clear a few things up, Atlanta's city population now stands at about 540,000 people (the highest it's ever been)...whereas metro Atlanta is up to (gasp!) 5.4 million people. That means only 1 in 10 ppl who live in metro Atlanta actually lives in the city. In 1990 the ATL's city population dropped below 400,00 so this is a city on the rise that is now repopulating itself. It's already surpassed it's 1970's peak of nearly 500,000 people. Metro Atlanta, meanwhile, is the nation's fastest growing metropolitan area, so don't be surprised to see it surpass Houston at some point.
St. Louis, on the other hand, once peaked with a city population of over 850,00 people. Currently the city population is down to about 355,000 though the metro area is home to over 2.8 million people. Still, the city population of St. Louis represents the typical kind of drop you see in a lot of the rustbelt/Midwestern cities - Cleveland (once home to over 915,000 now down to about 470,000), Pittsburgh (peaked at close to 700,000 now down to about 310,000), and especially Detroit (city population peaked at 1.85 million, now down to 910,000).
Midwestern cities like Columbus, Oh, and Indianapolis are lucky in that they've managed to buck the trend, and were able to avoid seeing their inner cities crumble. Columbus is up to 754,00 and a metro area of 1.7 million, while Indi is up to 800,000 in the city, and 1.7 million in its metro area (2 million if you add the Combined Statistical area).
Important distinctions between Indi and Atlanta include the fact that while only 1 in 10 ppl who live in metro Atlanta actually live in the city of Atlanta, over in Indianapolis about half the metro area lives in the city. At the same time, Atlanta is about 130 Square miles in size versus Indi being 370 Square miles in size, about 3 times as much. Furthermore, while metro Atlanta is heavily spread out over 28 (!!!) counties, if you look at a map of metro Indi you'll notice that most of the suburbs form a ring that surrounds the immediate area around the city in all directions.
Lastly, someone mentioned a couple of major cities in Texas. Houston’s city population stands at over 2.2 million people, and its metro area is about 5.7 million. Yet the size of the city of Houston is HUGE at about 600 square miles (compare that with Indi’s 370, or Atlanta’s 130). The overwhelming majority of the ppl living in metro Houston, 4 million, live in just one county – Harris, which of course is where Houston sits.
Dallas has a city population of about 1.27 million, which in and of itself is far bigger than that of the city of Indianapolis (800,000). In fact, Ft. Worth, which is part of the Dallas metro area, has about 720,000 people, and will likely exceed Indi’s population in the coming years. The size of the city of Dallas is a bit bigger than that of Indi at 385 Square miles, while Ft. Worth is smaller than Indi at 300 Square miles. The Dallas-Ft. Worth metro area, aka the metroplex, is home to 6.3 million residents spread through 12 counties.