Drupal 7, GPS lat, lng closes value, is it possible?
Have a look at this article: Creating a Store Locator with PHP, MySQL &amp; Google Maps. Especially the section about "Finding locations nearby with MySQL" is hinting towards your solution.

As you can read in the mentioned  article, calculating the distance between 2 points given their lat/lon requires quite some math (Haversine formula). So, I guess that the performance optimization in the article you are referring to won't be possible. This because it will be hard to use an index to retrieve probable points.