Google Maps, local search engines, internet yellow pages and other online business directories often receive biz listing info from a great many sources and must merge it together (see my description of this in Eric Enge’s interview with me). When this happens, loads of variations in the business’s name, address and even phone number can cause listing data to fail to be merged. All this makes me think we might need a “Canonical Tag” for phone numbers! Read on, and I’ll elaborate…

Some business directories and data aggregators contain huge percentages of bad listings including gone-out-of-business companies and duplicated listings. Pankaj Mathur of InfoUSA recently estimated that some sources such as Dunn & Bradstreet, Acxiom, Localeze and Google Maps might contain 17-to-18-million records, or up to 4 million more records than actual, live businesses! That’s as much as a 28.6% error rate!

I know from experience that some percentage of a business directory’s bloat can be caused by inability to figure out if a business has closed up for good or not (most data sources are not set up to verify each individual business, although InfoUSA remains an example of the gold standard, relying on a practice of phoning each and every business to verify it’s viability at least once per year, and also using a number of other signals of possible closure). These old, dead business listings clog up a great many online directories and can result in poor usability when consumers attempt to drive to their doorsteps for products or services.

However, another source of bloat is in the form of duplicate listings, and as a search engine marketer, it’s these duplicate listings that my clients sometimes have which concern me highly. Just as with duplicate webpages in regular SEO, duplicate listings in business directories and within Google Maps can potentially dilute down a company’s possible ranking score, resulting in lower overall rankings and poorer online performance.

Back in February, Google and other search engines jointly announced support of a canonical tag for webpages, enabling webmasters to specify which page URL should be treated as the main/authoritative one for search engine indexing in cases where multiple URL variations could occur.

If such a protocol makes sense for the general web search engines, why not a protocol to assist in reducing dupes in local search, too?

Google Maps help suggests that users can help them identify cases of duplicate listings, but the problem is that dupes may be constantly coming in through all of Google’s various data partners.

At the recent Kelsey Conference, local directory industry experts predict that Cost-Per-Call is increasingly going to become a dominant pricing model and this will mainly happen through individual directories displaying different tracking phone numbers for the same businesses – and all these different channels with separate phones feed into Google Maps, Yahoo! Local, Bing Maps, and other local search engines. So, potential issues from many various phone numbers could be increasing.

Tracking phone numbers are not the only potential problem – sometimes a company’s alternate phone numbers and fax numbers will get parsed off into separate business listings, causing further instances of duplication.

So, how could this “Canonical Phone Tag” effectively be accomplished? hCard Microformat already provides a framework for doing something like this. A canonical phone tag could be formed like this:

<abbr class=”tel” title=”000.867.5309″>000.123.4567</abbr>

In this example, webpage users could see the “000.123.4567″ tracking phone number when they view the webpage, and the machines could instead glean the authoritative, canonical phone number for the business, “000.867.5309″, and ignore the tracking number.

So, is this a solution in search of a problem?

How many of you have encountered instances where a tracking phone number has gotten indexed in a separate listing alongside a business’s primary phone number/listing? If so, this solution may be worthwhile to consider in keeping all of a business’s ranking weight combined in one listing as opposed to distributed across many.

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