Detroit - 993,078 - 77.9 sq. mi. - 12,748 ppsm
Milwaukee - 457,147 - 25.3 sq. mi. - 18,069 ppsm
Atlanta - 200,616 - 26.2 sq. mi. - 7,657 ppsm
Grand Rapids - 137,634 - 17.5 sq. mi. - 7,865 ppsm
I don't know about you, but I would definitely say Atlanta had a lot more in common with Grand Rapids than it did with Milwaukee or Detroit. It was definitely a larger and more important city than Grand Rapids, considering that it was the capital and largest city in Georgia, but on a relative scale, its closer to Grand Rapid Rapids than it is to other large Midwestern cites. I guess a better comparison would have been Columbus or Indianapolis, but even those cities were larger than Atlanta in the 1920's.
Atlanta's downtown core has 40+ highrise buildings from 1900-1920's, the oldest being the Flatiron Building built in 1895. There is a large neighborhood downtown called Fairleigh-Poplar that is nothing but historic buildings; then there is Castleberry Hill, which is an 1800's industrial/warehouse district that is booming with residential and retail loft conversions; the Marietta St. corridor is another 1800's industrial district, with retail and residential lofts. These comprise a huge part of downtown and I'm sure can compete with Milwaukee. In 1920 Atlanta's population was 200,000 to Milwaukee's 457,000...Atlanta was smaller, but still a large city for that time period. There is a large amount of history here that is often overlooked by people who have never visited and make assumptions that Atlanta is a "new" city. Oh, and Grand Rapids population in 2000 wasn't even as large as Atlanta's in 1920, so definitely not a good comparison.