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Having been in this industry for as long as I have, I often forget some of the basics. Well, it's not that I forget, it's just that I assume that everyone else in the industry has the same knowledge level as I do.

So when I get a 'newbie' asking a question like 'Why are my Google results different than my clients' I have to take a step back and realize that we aren't all equal.

Therefore in this article I'm going to answer this one seemingly simple question. While it may be simple to those of us 'in the know' this isn't always the case with others.

One of the scariest things you can do as a new SEO is talk to a client. That's because you are always worried that they are going to ask you a question that's over your head. And while you can fake your way through some questions when you are new, there are some that just stump you.

Of course even the greenest of most SEO's usually know more then their clients so you don't often have to fake an answer. Of course I would never advocate faking it. When I don't know, I've found the best thing you can say is 'I don't know, let me find out and I'll get back to you.'

And that's just what happened the other day. A new person came to me and said 'I had a client who saw different Google results than I did, and I didn't know what to tell them.'

So let me give you the answer I gave him.

Google, like all the other engines, is comprised of literally tens of thousands of servers. Each server is part of a larger cluster of computers. Each cluster forms part of a datacenter. Each datacenter then acts as an independent branch of Google.

These datacenters are found all over the US. For the longest time Google only had about 13 data centers that served all the results to the world. Now the number is estimated at around 80.

While some of these data centers are used for pre-testing results (for example, testing a new algorithm out before moving it to the main data centers) most are used just to deal with the load that Google receives every day.

These data centers are dispersed throughout the US in geographically specific areas. They have done this so that queries are served to the data center nearest to the user.

For example, while there are a large number of data centers on the eastern coast, a person searching from San Francisco will likely be served their search results from a data center near them, such as an Oregon or California data center.

It is because of the differences in these data centers that someone searching in New York will see different results than someone in Los Angeles.

It is reasonable to think that each data center acts somewhat independently of the others. That means that their update schedules are different as are their crawling schedules. One can even assume that the algorithm changes which affect the index happen at different times as well.

This accounts for why there are differences in search results. Because of Google's perpetually updating index, the results you see near you may be similar to results in other data centers but ultimately different.

This could be due to how the crawlers retrieve sites - a crawler may find a site closer to it more easily and therefore add it to the index sooner than a geographically far away crawler would find the same site.

For example, a site in Vancouver, Canada may appear in the California data center days before the eastern data centers. Because this site would be added to the west data center sooner, it will have an impact on the search results returned sooner.

Consider it like the ripples you see in the water when you drop a rock into a pond. If you drop just one rock, you see the ripples move out from where you dropped it. However, if you drop 2 rocks close to each other and at slightly different times you see how the ripples interact with each other when they meet.

The index changes reflect this type of interaction. One site can have a subtle but noticeable effect on the index. Yet the effects aren't noticed across all data centers at the same time. We can also see the changes in the index grow over time, so that one Vancouver site's effect grows over time, but the effect is different across the data centers because changes happening with other sites also has an impact.

As you can see, this is why you will see different results across the data centers. It's not necessarily because of one single event. Like SEO itself, it's a culmination of smaller events which causes the noticeable differences.