New York covers much of it except for a 51 mile opening to Lake Erie.
New York and Lake Erie. Mason Dixon Line
the country that forms the northern boundary of the United States is Canada :)
This is the boundary with Ukraine: mountains and the river Tisa.
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
To the north of Pennsylvania, the state of New York borders its northern boundary. Additionally, Lake Erie forms part of Pennsylvania's northwestern border, while the southern shores of Lake Ontario are also within proximity to the northern part of Pennsylvania.
The Arctic Ocean
red river
The sea that forms the northern boundary of Africa is the Mediterranean Sea. The countries of Morocco, Algeria, Tunisia, Libya and Egypt border it.
Most of the northern boundary is formed by the Alps. However, on the Iberian Peninsula, the Pyrenees form another northern border of Southern Europe.
The Delaware River forms the boundary between Pennsylvania and New Jersey.
Mediterranean Sea
The river Danube and the South Dobrogea.