That map is showing the Atlanta media market, which is much larger than any definition of metro Atlanta that I've ever seen. The metro definition varies, but the most common one is the Census Bureau's Atlanta-Sandy Springs-Roswell MSA , which includes 29 counties: see
http://www.metroatlantachamber.com/docs/default-document-library/29-county-msa-map-and-text42913.pdf for a map and list.
The MSA has about 5.7 million people, which is a little over half of the state population. I'd guess the larger area shown by the media market probably does approach 2/3.
