One of the early promises of the internet was that national marketers would be able to target on a local level with greater precision (not to mention with interactivity featuring sight, sound and motion) than existing offline media such as community newspapers, radio stations, direct mail, telemarketing and, in larger markets, local TV.

Local targeting is not easy. The only way to determine if someone is sitting in Miami instead of Los Angeles or Boston is to track their regional ISP address. That can be kind of tricky since some ISPs (like AOL) have a national footprint, while others (like my own Cablevision) cover multiple states (I am told there are various access points within a large ISP footprint to further narrow your location, but I don't think they are being used for targeting at this juncture). In addition, the large portals like Yahoo! and Google have registration data that includes your ZIP code, so they have some idea of where you live and probably access the internet. But if that creeps you out, rest assured that the Big Boys can't target with that kind of precision-- yet. In fact, they are having some problems, like this example of an ad for a California proposition served to a lower Manhattan, NYC newspaper.

The most reliable way for national marketers to deliver messages into local markets is through local market websites (or the localized content sections of the portals, such as weather). If you think about the local sites in your area, many of them are poorly trafficked either mom and pop retailers or community/municipality sites that give you information about parks, schools and the library. The sites that really get traction are companion sites to local media properties: radio, newspaper, TV stations. One can reasonably deduce that visitors to these sites live and work in the area or have an abiding interest from a distance (maybe they are ex-pats keep up with the local news or plan to move to the area).

This, then, is the reason why ad networks that specialize in helping national advertisers target locally have grown up by aggregating numerous local media sites. If you have the ability to sell some inventory for a couple of local TV stations and radio stations and the newspaper, you can deliver an audience that is pretty reliably local.

"If you look at many of the portals' local news offerings, you may get one or two stories. With local media sites, because the news is more relevant, not only is there a lot of rich content, it comes from trusted anchors and news sources within the market," says Allison Bodenmann, EVP National Sales for WorldNow's Local Media Network.

Let's look at some of the major players in this space.

If you want more thoughts on general interest networks and local capabilities, check out the last page.

Author notes: George Simpson works with new media companies to help them tell their stories and promote their brands. Read full bio.