>>Latitude and Longitude are universal coordinates http://en.wikipedia.org/wiki/Latitude
>
>Thanks, so if there is only one way of storing coordinates, what is the difference between "Latitude and Longitude" and "Latitude and Longitude in radians"?

It's either 0-360° or 0-2PI in radians.

The proximity search is very well explained in the link http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/sql-server-zipcode-latitude-longitude-pr