If you are going to use direct mail as the engine that runs your seminar program, you have to be able to determine what area to saturate with invitations. The first thing you have to do is to figure out which zip codes to mail to. It's very simple: go to www.zipfind.net and click on "zip find deluxe." On the right side you will see "radius search."
Simply put in the zip code of the restaurant you're using and select six miles. This will give you a list of all the zip codes within a six-mile radius of the restaurant from closest to farthest. Remember that prospects will drive a maximum of 15 minutes to go to your event. So if you live in a rural area it might take 15 minutes to drive 10 miles, or more in an urban area.
At this point you have a list of zip codes to mail to. You will notice that some of the zip codes will have a population of zero, so obviously you don't need those. I would suggest making a list of those zip codes, from closest to farthest, and send them to the direct mail company that will be printing and mailing out your invites, as well as some information about the demographic you hope to reach. They can do the research for you.