>>There's also this http://geocoder.ibegin.com/downloads.php
>>
>>US zip codes with longitudes and latitudes
>
>Thank you, this is useful.
>
>I have a class that calculates the distance based on two sets of coordinates. However, I am still curious to know how they do it to calculate so fast that x number of records correspond to a 50 km radius, from a specific location, taking from a 10,000 records table.

Some things come to mind

(1) They may also store the lattitude in radians to speed up the calculation
(2) They may have a table that stores all the distances (and update it within a trigger if the coordinates of a city are changed/added)
eg 10,000 cities would be a table of 10,000 * 10,000 / 2 records = 50,000,000 records