In ruby i found latios on my pokedex but i flew there he was at a different place and he kept doing that.Does that happen in emarld ?
if you try to fly to latios he will move to a new spot you can only ride yur bike swim or walk but no flying
swimming walking or bikeing doesnt work everytime you go to a new area latios/latias will change areas also.
Heres a tip on how to catch them though.
Go to any area (except towns) and look at were he/she is. then go one route down or up and hell be at a new area look at your pokedex again and if hes/shes not there then go to the route you were just at. keep repeating untill hes in the area your in (it may take a while) then as long as you stay in that area hell never leave. (but usally hes the first pokemon youll find)