Geographic data

How is it done

[graywolf]

I have seen some sites where you are searching for something and you put in your zip code. You can then specify how many miles away you would like to search (5 miles, 10miles, 15 miles, etc). How and where do you get the data to know how close one zip code is to another?

[jcoronella]

There are several free zip code databases out there, and most have longitude/lattitude information that you can use to calculate distance.

Should be easy to search for a longitude distance calculator as well as free zip code database.

[choster]

Check the "freshness" of those databases. ZIP codes change, especially in areas of high population growth.

For instance, Ben Fry's "zipdecode" visualizer, which you may have seen, fails to recognize some 928xx codes that were remapped from 926xx the better part of a decade ago. We are not talking about some small town, but hundreds of thousands of people in Orange County, California. Not a big concern for Fry, as his site is a simple demo, but for a commercial website I'd be extra careful.