If you’re looking at a map, when does east become west—and west become east?
It depends on how you look at that map, according to Rob Ferry, senior cartographer with Rand McNally of Skokie, Ill., a company that has been creating maps, guides and navigational tools since 1869.
The Aleutian Islands, for instance, stretch 1,200 miles westward from the Alaskan coastline, and demonstrate this geological measure. The islands closest to the mainland are located in the Western Hemisphere, while those farther west spill into the Eastern Hemisphere.
Cartographers offer two ways of measuring America’s eastern and western geographical extremes.
By travel, the easternmost point of the United States is Sail Rock, Maine. By degree of longitude, the easternmost point is Semisopochnoi Island, Alaska (sited at 179 degrees east longitude).
By travel, the westernmost point is Peaked Island, Alaska, which is in the eastern hemisphere. By point of longitude, the westernmost point is Amatignak, Alaska, which is in the western hemisphere.
What does “degree of longitude” mean?
That’s the geographic coordinate used to chart distances east and west. Two imaginary lines play key roles in this calculation: the Prime Meridian (at zero degrees longitude, the meridian runs through Greenwich, England), and on the other side of the planet, the 180th meridian, the counterpart to the Prime Meridian. The two points where those meridians touch divide the globe in half: into the Western Hemisphere and Eastern Hemisphere.
Latitude lines help chart north and south sites. Those are measured north and south from the Equator.