Robert Kirkman, who has written all of The Walking Dead comics and is also involved with the TV show, is a man who originally hails from Kentucky. Keeping that fact in mind, it's easy to see why Robert Kirkman decided to mostly avoid an urban setting while writing his comic series. He recently explained why The Walking Dead is set in Georgia in a recent interview. Here's what he had to say:
I didn't want New York, LA or an urban setting. I didn't want a supercop, the president or CIA guy involved. I wanted ordinary people at the center, in the thick of it, just trying to survive, get by and do right by their family.
While AMC's version of Rick Grimes has him living in Georgia at the start of the series, The Walking Dead comic actually kicks off in Kentucky, where the Grimes family in the written world actually hails from. In the comics, after Grimes wakes up from a coma---similar to the TV series---he learns his family may be in the Atlanta camp and makes the journey to reach them. Eventually, he becomes the leader of a ragtag group of survivors, much of which the AMC drama has faithfully adhered to. Of course, there are plenty of changes from the comics, but the core premise and setting remains very similar. Robert Kirkman also told the Richmond Register he never thought either the comic series or the TV show would last. In fact, they both have thrived.
The southern setting for the series has certainly helped the AMC drama to set itself apart from a lot of other TV shows. While there are a million series set in New York, Los Angeles and---thanks to Dick Wolf---Chicago, the woods and wilds of Georgia makes for an interesting location to complement the intriguing nature of the series, which is essentially about surviving in a world filled with zombies. It really helps to give The Walking Dead an edge over other zombie shows that are on TV or have aired on TV.
Of course, while Robert Kirkman did try to strip down The Walking Dead and make it more about ordinary people in extraordinary circumstances, it wouldn't be fair to just gloss over the fact that the large but abandoned metropolis of Atlanta is a setting the TV series explores early on. It's also relevant to note that the spinoff drama Fear The Walking Dead initially earned buzz for being set in Los Angeles, which is one of the big cities Kirkman is mentioning wasn't a good fit for his parent series. While the show has moved on from its initial setting, it is curious that the big city seemed to work for the initial part of the outbreak. It proves that zombies in big cities can certainly work; that just wasn't the story Robert Kirkman initially wanted to tell.