While people love to talk about link popularity and search engine rankings, they rarely talk about one of the more common problems with link building. In a nutshell, unless the links to your site exist on the first or second directory level of the linking site, they likely won't impact search engine rankings.

The technical term for this is "link depth origination". A search engine's crawler/bot indexes your web site (or anyone else's) only to a certain depth and then moves on to the next site. The depth a search engine crawler will go varies from engine to engine and even varies for the same engine from day to day and URL to URL. However, most crawlers go no deeper than three directory levels into any given site, like this. (yoursite.com/level-1/level-2/level-3/).

In looking at your server logs, you may find instances where a crawler has gone deeper than level 3, or shallower, but the point to take away from this is if a link to your site is on a page on the originating site that is deeper than the third directory level, the crawlers will never know the links exists. The link is deeper than the crawler crawled.

Not to mix metaphors, but imagine fishing on a lake that's 100 feet deep with a net that can be lowered only to a depth of 50 feet, and you get the picture. Anything that's deeper than 50 feet is not going to be caught by the net.

This does not mean that such links are worthless. It means only that such links cannot be factored by the engines into the engines' link popularity measurement. They can't factor what they don't know exists.

This raises an intriguing scenario. Imagine you have two sites with nearly identical content. Site A has 500 sites linking to it, but all 500 sites placed those links beyond their third directory level.

Site B has 25 sites linking to it, all of them at the highest (top) level directory.

Which site, A or B, is better positioned from a linking standpoint?

Well, it all depends. What kinds of sites do the links exist on? Those 500 links to your site will be useless if they originate on random link lists with no content and no page views, or if all those links were beyond the third directory level on the originating site. Likewise, site B with only 25 links may be getting nice new traffic if all 25 links originated close to the surface (top level) of well-trafficked, topically relevant sites.

This is an extreme scenario. It's more likely that your site falls somewhere in between. You have some good links, and you have some useless ones. You usually can't control where the originating site places its link to your site. If I have a links page that is four directories deep on my site, then even if it's the most useful links page in the world, none of the search engines are going to find it.

Let's sum all this up in a list of key points.

• If your goal is to improve link popularity, the links to your site need to originate as close to the top level on the originating site as possible.

• A link originating beyond the third or fourth level is still important if the originating site is topically relevant and useful. Yahoo! is a good example. Most sites linked by Yahoo! originate far beyond Yahoo!'s third directory level. My own Yahoo! listing is five levels deep, yet sends me hundreds of visits every day.

• A few purposeful links are better than many non relevant laundry list link lists or Free for All Links Pages.