This is feature for paying members only and it lists the cachers, who found most of the caches in some area. From the page:
This top list shows who has the highest percent found in an area. Hides will count as found in this case, events and archived geocaches will not be accounted for.
It is useful for for competing in some small areas (city/county), with your friends living and caching nearby.
http://project-gc.com/Statistics/TopFoundPercent
