Location Based Searches

[eluser]TornUp[/eluser]
Hi All,

Haven't posted on her alot, but am a massive fan of CI!

My Question is not 100% in regards to CI(but it is the framework im using to build the system)

My question is in regards to how dating websites(as an example) and websites such as autotrader(second hand cars) are able to allow searches in a "10,15,30,etc.." mile of your postcode/zip-code, and how one would go about developping a system like that.

iv googled the topic, but it brings up "location based searches"(searches based on my phisical location, like "bars near me now")

i hope your able to help!

Thanks In Advance!