Nice little article about it - http://www.pastemagazine.com/article...-spin-off.html

“We didn’t want to do CSI,” says Greg Nicotero, The Walking Dead’s make-up effects guru, producer and frequent director. “We didn’t want to do a cookie-cutter show that was the exact same thing.”

What comic-book creator Robert Kirkman and his team of producers did instead was to go all the way back in time before Rick Grimes wakes up from that coma, before the zombie apocalypse had turned every city into a nightmare-scape, and look at how the collapse of civilization affects a family in an urban setting.