There are certain types of Web applications that can benefit from knowing the exact geographic location of their users. Some of those applications could for instance tell about resources of the interest of the users that are located in their neighborhood.
Most users are not able to tell where they are located, but usually they are able to tell what is the postal zip code of their region. Each zip code can be associated with the approximate geographic coordinates of its region.
Locating resources near the region of an user is a matter of determine which zip codes are located within a reasonable limit distance from the zip code informed by the user.
This class provides a solution this problem suitable for sites of users living the United States. It consists in looking up a database of coordinates of zip codes to figure which other zip codes are located in the same region.