zipcode radius search?

Question

Okay I am trying to create a site that finds users within a certain distance of their zipcode.
There are roughly 42000 zipcodes.

When a user creates a request to find people within a 100 mile radius of their zip do I...

either...

1/ Seacrh a zipcode dtabase that contains long and lat, calculate all zips that are within 100miles of their zip (this would require 42000 calculations) and then search all the users with the selected zipcodes.

or

2/ Do I already have a database with every zipcode within a hundred miles of each zipcode. Therefore, when a user requests users within 100 miles, I can simply select the 10 mile radius zipcodes for that users zipcode.

Or am I completely wrong. How do sites like myspace find users within a certain radius of a zipcode?

Thanks to any responders.

Answer 1

Number 1. Good thing, many others have done this before, so it depends on your data set and programming platform.

http://www.kevinroth.com/projects/project.asp?id=85

ie
http://forums.mysql.com/read.php?23,3868,3868