Also, how would the Dead Zone be "above" the former NYC area? Assuming "above" means "north of" (which is sloppy anyway), nobody from Arkadia/TonDC would have to pass north of NYC to get to Becca's Island (south of Long Island, east of NJ). Not sure who added that, but it makes far more sense for the Dead Zone to be in an area between NY & DC, probably including NYC judging from the S2 opening credits.
If the Delphi clan of Grounders are from the former Philadelphia, which is what I'd figured, the Dead Zone may start north of there. But it logically must include at least part of NJ, south of NYC.