The Appalachian Mountains (or Appalachians) are a vast system of mountains in eastern North America. Definitions vary on the precise boundaries of the Appalachians. The USGS defines the Appalachian Highlands physiographic division as consisting of thirteen provinces: The Atlantic Coast Uplands, Eastern Newfoundland Atlantic, Maritime Acadian Highlands, Maritime Plain, Notre Dame And Megantic Mountains, Western Newfoundland Mountains, Piedmont, Blue Ridge, Valley And Ridge, St. Lawrence Valley, Appalachian Plateaus, New England province, and the Adirondack provinces. A common variant definition does not include the Adirondack Mountains, which are often said to have more in common with the Canadian Shield than the Appalachians.