Basically if you request a search at google it will check your geographic location by your IP and depending on its value different search results will be served.
If you use a local google engine for instance google.co.uk, you will see that many site with co.uk will be listed high, because their geographic target match your location.
These are the major aspects which are considered when google calculate the different 'local search results':
- Use of national domain eg. co.uk
- The IP of your webserver
- The language meta tag
- Geographic classification of the domains which link to your site
Otherwise you may set your preferred geographic target location at Google sitemaps.
Thank you