Digital has great localization technology that gets better every day. But a few things need to happen in order for it to fulfill the role of a true spot medium. Here's why.

I think it's highly ironic that within the digital landscape, we can geo-target online ads to the ZIP code level, but we still have yet to see digital emerge as a true spot medium.

There are a number of strategic roles for spot broadcast media. I don't see digital delivering on those strategies often. For instance, it's a common media strategy to adopt a market-specific approach, looking for DMAs in which there is an opportunity to snag share from a competitor. A national brand might pick a handful of markets where their BDIs are outpaced by their CDIs and, smelling an opportunity, bolster their spot spending in those markets.

A national brand might also use spot media to even out the delivery of a national plan. National advertising plans have skews to them, and sometimes the delivery of a given buy impacts certain markets less than others. A spot media strategy might look at each DMA and lend spot support to ensure effective reach.

Spot can also really help when it comes to limited market tests that can steer creative, media or marketing strategy for national plans going forward. There are dozens or even hundreds of reasons why a national advertiser would want to strategically use spot media.

But why isn't digital typically a part of spot strategies? If we can geo-target in digital better than we can in almost any other medium, why doesn't digital have a tremendous influx of spot dollars?

It's a scale problem. (Sound familiar? We've seemingly got scale problems all over this industry.) The mechanisms by which buyers can quickly put together a top 50 DMA media plan for TV, radio or cable are all in place and easily implemented. Offline spot tasks are simpler -- a market might have a handful of radio stations that can deliver efficiently into the market. Buyers know what they are, and they can buy efficiently and easily in a currency (GRPs) that everyone involved understands.

We're used to digital spot buying being anything but simple. There are a lot more vehicle types involved. There are global portals that can geographically target ad inventory. There are local sites, and online companions to offline local news outlets like TV stations and newspapers. These vehicles don't neatly fit into buckets insofar as their content is concerned. A spot radio buyer can look at a station and know that ACH means the station plays adult contemporary music, or that AOR means the station plays album-oriented rock. No such luck for the digital spot buyer, who deals with sites having a wide range of content or no content focus at all. 

To compound the difficulty, each media outlet might geo-target its inventory via a different method, which has significant implications for out-of-market spill. Notice that we haven't even gotten to a discussion about weight levels and cost efficiencies yet, and we're already confused and off-track.

Is it any wonder that digital really isn't on the radar of a lot of national advertisers who buy spot offline?

I think figuring this out falls to companies like Centro. A few weeks ago, the company made a splash when it snatched up Real Cities from McClatchy. However, I think the strength of Centro's offering lies in its platform, which gives agencies and advertisers planning and buying tools to help address many of the challenges I outlined earlier, as well as a few others, like reconciliation, billing and reporting. What Centro is in the process of doing is applying its tools to fulfill the strategic promise of digital spot media.

If you ask me, Centro is an acquisition target for the likes of Google. Google's bottom-up approach to local advertising gives it tremendous strength, especially with small advertisers. But what Google doesn't have is a platform that lets leading national advertisers buy spot media in the way they're used to buying it offline. Snatching up Centro should be a no-brainer for Google.

Regardless of whether an acquisition is made, though, what we're seeing is the development of the spot market for digital. If you're an advertiser who has been wondering how long it's going to take digital to get this figured out, wonder no longer.

Tom Hespos is the president of Underscore Marketing and blogs at Hespos.com.