The Taxpayers Association of Central Iowa’s annual symposium will be at 7:30 a.m. May 14 at the Greater Des Moines Botanical Gardens, 909 Robert D. Ray Drive. Abir Mandal, co-author of “Securing property tax relief in Iowa,” is the keynote speaker. Mandal is a senior policy analyst at the Washington, D.C.,-based Tax Foundation. Mandal will…