Tipping-Point Power of Linking
SeachReturn recommends a cautious link building strategy which encompasses tactics that obtain natural linking, and generally avoids link buying from all sources that sell them, (short of those that deliver traffic in a media-buying sense). Links in private areas of a site won't get noticed by search engines but can deliver volumes of high quality traffic. Judge the merit of the link purchase by the volume and quality of the traffic it delivers. Have no concern if the "nofollow" attribute were applied when considering the purchase of a link, thinking of it purely in the media-buying sense (never for search engine rankings).
The main things to consider with link building is where to have them point, and (if you can influence the text used) the text in and immediately surrounding the link container. If you operate several sites, there are search engine guidlines against the practice of doing so in order to flood search results. Although this can be effective for spammers, they push products where being removed isn't an unrecoverable disaster. Don't copy the tactics of highly ranking sites that are only destined to get removed. If your business is too important (and sensitive to getting removed), these guidelines are a vital source of information.
However, there is a far better reason than search engine guidelines where it makes sense to publish one primary site for search engines, and to relegate other domain properties to campagins outside search. Think of it in terms of a Tipping-Point linking strategy. Extra ranking power is associated with an authority site that has a large number of quality links giving it a Tipping-Point advantage in rankings. The same links do not add up to the visibility power of the whole when spread thinly across more than one site. The whole is larger than the sum of its parts.
Consider a widget company "A" owns one site with 100 quality links pointing to it giving it a link rank of 8, and widget company "B" owns 10 domains with 10 links each (from the same set of 100 links). Each site in case B has a distributed link rank of 2 or 3 out of the whole number 8. The Tipping-Point fact is, company A will be found in competitive keyword areas (and is broadly visible), where company B will be lucky to rank at all against sites with higher link rank. Since search users rarely advance past the first few listing pages, company B sites in total will suffer from poor visibility and will underperform compared with company A.
Concentrate your link building efforts with a primary site, and redirect or disallow robots to the other sites. For rankings in natural search results, work to get your main site indexed so users will tend to find it and link to it versus scattering the innate power of Web linking across multiple domains. You can use your other domain properties for offline media advertising such as direct mail, print, radio and television. You can also run specalized PPC campaigns with them (although webmasters that discover one of these sites would not link to the best domain).
If you have more than one topic area, use directories instead of sub domains. This concentrates linking power rather than fragmenting it inside the site. The Tipping-Point Power of Link Building is far too important to split apart. Sub domains are too often used in cases when they are absolutely unnecessary. Even worse, sub domains are suspicious as they are very frequently taken to the extreme by spammers.
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