I assumed that it would be taking place in Salem since that's where the biggest witch community would be. Thus, they wouldn't be alone, they have access to many necessities that are required for witchcraft such as vendors for reagents and materials or places/beacons of increased power[sub]or something[/sub]. But I guess you could make your character be wherever they want haha :p

EDIT: Also, as a hunter, you'd wanna be where the action is right? 

I based my character around the Massachusetts area anyway :D

EDIT EDIT: I'm assuming hunters have their own tricks and such to find out about witches. For example, Natalia is described to be a great researcher so she's probably familiar with all the bloodlines and what type of witchcraft that they delve into. Thus, she can use that with some sort of combined equipment to find out the placement of a witch. But you could also follow news leads that are incredibly sketchy or publicized events that seem to fit in a more supernatural setting that normal people don't understand.