Forum Moderators: skibum
Once you know this, there are any number of professional Direct Marketing firms that can help you target your mailings by geographic area.
One word of advice though, lists targeted by interest will always yield greater results than those targeted by geography alone.
Lets say I have a hot widget that is popular among California college students. I can slice the data by City for "Population 18 to 24 years--Percent enrolled in college or graduate school". Find out what colleges are in those cities and advertise in their school paper.