Search engines use complex algorithms that have hidden criteria, which weighs up a website to see how relevant the website’s content is in comparison to the search engine’s image of how the most relevant site should be. Some elements in the formula have more weight than others, meaning that they are considered to be more important in determining a rank the website will be rewarded with. However the algorithms are kept in secret. Nobody, except people employed by the search engines, know how the algorithms work
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Some search engines use the actual geographic location of a web server as an indicator of the geographical market that is being targeted by a website. Therefore, it is advised to host your website on a server located in the same geographic region as is targeted.
Another indicator of the geographical region is the domain extension such as .com.au .co.uk .ca etc. If you target worldwide audience it is desirable to get domain name with .com or .net extension.
You can also use sudomains and a separate server for each geographical area. For example, http://uk.yourdomain.com subdomain can be hosted on an UK based server.