I have maintained a Big Tree database for the City of Parkersburg, WV (7000 acres, 30,000 pop.)for the past seven. years. We accept written and online nominations year round and award certificates for the biggest their species. Awards are usually held in conjunction with an Arbor Day event. Participation has varied from six to forty-five submissions. As a result we keep a Big Tree database on the city website (link below)http://www.parkersburgcity.com/treecommission/downloads/2015-Big_Tree_List.pdf
My policy is use AF measuring standards and maintain a list of trees with the three biggest point totals plus the tallest, largest CBH, and largest spread if not included with the largest Af point trees, List is updated yearly.
Some advice: Only include measurements from yourself or someone you have trained. If you have the means run your own website. My experience with the city is Ok except changes and corrections are very slow. I intend to make it was a county wide effort since we get a lot of submissions from the surrounding Wood County. Consider that your species ID will have to be upgraded to word wide. One some of my first ID failures were a result of missionaries returning from overseas and planting some obscure (to me) species. Hope this helps