Below is a map created by Grant Sutherland which breaks up Peachtree Corners into its three Posts. Check it out, or click the link to be able to put in your address and see which post you are in!
You can also consult the official City Map, found here
Finally, the city clerk has the official registered voter list, which lists your post according to your address.
Feel free to contact me if you have any questions, and go Vote!