"All MapQuest Advantage Enterprise and API customers can use custom SQL WHERE clauses to limit database queries. Use database connectivity to:
- Find and/or display locations within a specified radius.
- Find and/or display locations within a specified rectangle.
- Find and/or display locations within a specified polygon.
- Find and/or display locations around a path, such as a route (suggested driving directions).
- Search with a simple database record MapQuest API, new in version 3.0. You can even access non-MapQuest-specific database fields.
- Integrate location data sets with other corporate databases. For instance, an application could filter bookstore proximity search results based on book availability determined through dynamic database searches."
Looks like a quite thorough API. We also learn that MapQuest.com "receives more than 26 million visitors every month and serves up over 10 million maps and directions each day."