>>>>>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
>>
>>Calculating the exact distance for every possible 'destination' seems like overkill?
>
>I don't know. Michel was wondering why it was fast.
>
>Of course you can 'heuristically' limit the candidates based on latitude and longitude
>
>But then, if there are only 10,000 cities, I wonder which will be the fastest method - I expect the 'overkill' will

Might depend on what Michel actually wants to do with this. Most likely only expecting a small result set (e.g. 'gas stations within 50 miles' type of thing). And if, for example, you're trying to estimate driving distance then a great circle route may not be more accurate than a cruder approximation....
But it sounds as if Michel doesn't have a problem with performance anyway....

>
>>If this is for the U.S. and only targets within a certain radius are required you could get a rough selection based simply on latitude and longitude.
>>There's pretty much a direct correlation for latitude (110 miles per degree) and given that the the U.S only extends from about 45-25 degrees it will always be between say 80-100 miles per degree of longitude. So grab the max by allowing an extra 20% on longitude then do the exact calculation on that result set? Not having the meridian pass through the country makes it easier as well.....