Make a separate object for each level, for example:

 map_file mine_mine_mine.map
 map_obj 1sig map_par 30 30 30 12 blue ;; ma_ac ma_dr
 map_obj 2sig map_par ; 24 green ;; ma_ac ma_dr
 map_obj 3sig map_par ; 36 red ;; ma_ac ma_dr