Actually there isnt higher lvl areas per se. Just that certain mobs have higher scaling options. IE, some mobs can be up to 15 lvls higher than your and some can only be 5 lvls higher. And every single mob scales up whenever you lvl up. Up to the lvl 50 though. After that mobs dont lvl up at all.
ah well just mean, like in the beginning of the game if you go north into the snowy fields, youll almost only find tougher enemies. But yeah.