Building links is an art
 

Building links is an art. It's almost certainly the most challenging part of an SEO's job, and, for many sites, the one most critical to achieving long term success. Many companies can afford to hire SEOs to help make their websites search friendly and search optimized, but a robust backlink profile is an extremely high barrier to competition.

As with any marketing activity, the first process undertaken in a link building campaign must be the creation of goals and strategies. Sadly, link building is one of the most difficult activities to measure, particularly from a search engine optimization perspective. Although the engines internally weight each link precise, mathematical metrics, it's impossible for those outside of the engineering team at these companies to extract this data. Thus, as SEOs, we rely on a number
of signals to help build a rating scale of link value.

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It is an art, and what art it is. Even with measuring the number of links (of a site), it is difficult to sum up because there are many different types of links; some valued higher than others. It is interesting to look at a site's profile and estimate the link profile. The profile reveals traffic and authority of a site. So much to learn.

Not a big deal coz entire technology has evolved from art.