There are two parks that make up the Universal Orlando Resort - Universal Studios (the original park) and IOA. WWoHP first opened in IOA, but now there is going to be the "expansion", Diagon Alley, in Universal. You would need a hopper ticket to visit both if you only go one day. Otherwise, you'd need a 2-day ticket
Correct..ALSO keep in mind, in order to ride the new HOGWARTS EXPRESS ride that will connect both parks ( it is an attraction as well as transportation) , you will NEED A PARK TO PARK TICKET( equivalent of a park hopper) , a single day , single park ticket will not allow you access even if you have 2 days to explore both areas